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This paper summarizes the evolution of mechanical tolerancing practices, the general character of tolerances as they are currently understood, the current state of tolerancing technologies, and the recent surge of activity aimed at rationalizing and “mathematizing” form tolerancing. The paper concludes with two examples that illustrate current research frontiers.

This article describes the aims and background of the RIDDLE project, which was funded by the Libraries Programme of the Commission of the European Communities' (CEC's) Telematics Research and Technological Development Programme. RIDDLE (Rapid Information Display and Dissemination in a Library Environment) started in February 1993 and ended in December 1994. A subsequent article will deal with the technical side of the project in more detail. Further information is available via World Wide Web at the following sites:

The action taken by the Council of the British Medical Association in promoting a Bill to reconstitute the Local Government Board will, it is to be hoped, receive the strong support of public authorities and of all who are in any way interested in the efficient administration of the laws which, directly or indirectly, have a bearing on the health and general well‐being of the people. In the memorandum which precedes the draft of the Bill in question it is pointed out that the present “Board” is not, and probably never was, intended to be a working body for the despatch of business, that it is believed never to have met that the work of this department of State is growing in variety and importance, and that such work can only be satisfactorily transacted with the aid of persons possessing high professional qualifications, who, instead of being, as at present, merely the servants of the “Board” tendering advice only on invitation, would be able to initiate action in any direction deemed desirable. The British Medical Association have approached the matter from a medical point of view—as might naturally have been expected—and this course of action makes a somewhat weak plank in the platform of the reformers. The fourth clause of the draft of the Bill proposes that there should be four “additional” members of the Board, and that, of such additional members, one should be a barrister or solicitor, one a qualified medical officer of health, one a member of the Institution of Civil Engineers, and one a person experienced in the administration of the Poor‐law Acts. The work of the Local Government Board, however, is not confined to dealing with medical, engineering, and Poor‐law questions, and the presence of one or more fully‐qualified scientific experts would be absolutely necessary to secure the efficient administration of the food laws and the proper and adequate consideration of matters relating to water supply and sewage disposal. The popular notion still exists that the “doctor” is a universal scientific genius, and that, as the possessor of scientific knowledge and acumen, the next best article is the proprietor of the shop in the window of which are exhibited some three or four bottles of brilliantly‐coloured liquids inscribed with mysterious symbols. The influence of these popular ideas is to be seen in the tendency often exhibited by public authorities and even occasionally by the legislature and by Government departments to expect and call upon medical men to perform duties which neither by training nor by experience they are qualified to undertake. Medical Officers of Health of standing, and medical men of intelligence and repute are the last persons to wish to arrogate to themselves the possession of universal knowledge and capacity, and it is unfair and ridiculous to thrust work upon them which can only be properly carried out by specialists. If the Local Government Board is to be reconstituted and made a thing of life—and in the public interest it is urgently necessary that this should be done—the new department should comprise experts of the first rank in all the branches of science from which the knowledge essential for efficient administration can be drawn.

Heat also facilitates the transmission of water through the cell walls, thereby assisting its passage from the interior to the surface of the material; it increases the vapour pressure of water, thus increasing its tendency to evaporate; and it increases the water‐vapour‐carrying capacity of the air. In the United States the unit of heat customarily used is the British thermal unit (B.t.u.), which for practical purposes is defined as the heat required to raise the temperature of a pound of water 1° F. Heat is commonly produced through the combustion of oil, coal, wood, or gas. Heating by electricity is seldom practicable because of its greater cost; but where cheap rates prevail it is one of the safest and most efficient, convenient and easily regulated methods. Direct heat, direct radiation and indirect radiation are the types of heat generally employed. Direct‐heating systems have the highest fuel or thermal efficiency. The mixture of fuel gases and air in the combustion chamber passes directly into the air used for drying. This method requires the use of special burners and a fuel, such as distillate or gas, which burns rapidly and completely, without producing soot or noxious fumes. The heater consists simply of a bare, open firebox, equipped with one or more burners, an emergency flue to discharge the smoke incidental to lighting, and a main flue, through which the gases of combustion are discharged into the air duct leading to the drying chamber. Direct‐radiation systems also are relatively simple and inexpensive and have a fairly high thermal efficiency. A typical installation consists of a brick combustion chamber with multiple flues, which carry the hot gases of combustion back and forth across the air‐heating chamber and out to a stack. The air is circulated over these flues and heated by radiation from them. The flues are made of light cast iron or sheet iron. The air‐heating chamber should be constructed of fireproof materials. The efficiency of the installation depends upon proper provision for radiation. This is attained by using flues of such length and diameter that the stack temperatures will be as low as is consistent with adequate draught. Heating the air by boiler and steam coils or radiators is an indirect‐radiation system, as the heat is transferred from the fuel to the air through the intermediate agency of steam. Such a system costs more to install and has a lower thermal efficiency than either of the other two systems. It is principally adapted to large plants operating over a comparatively long season on a variety of materials where the steam is needed to run auxiliary machinery or to process vegetables. Large volumes of air are required to carry to the products the heat needed for evaporation and to carry away the evaporated moisture. Insufficient air circulation is one of the main causes of failure in many dehydrators, and a lack of uniformity in the air flow results in uneven and inefficient drying. The fan may be installed to draw the air from the heaters and blow it through the drying chamber, or it may be placed in the return air duct to exhaust the air from the chamber. An advantage of the first installation is that the air from the heaters is thoroughly mixed before it enters the drying chamber. It has been claimed that exhausting the air from the chamber increases the rate of drying by reducing the pressure, but the difference is imperceptible in practice. Either location for the fan is satisfactory, and the chief consideration in any installation should be convenience. Close contact between the air and the heaters and between the air and the material is necessary for efficient transfer of heat to the air and from the air to the material, and to carry away the moisture. The increased pressure or resistance against which the fan must operate because of such contact is unavoidable and must be provided for, but at other points in the system every effort should be made to reduce friction. To this end air passages should be large, free from constrictions, and as short and straight as possible. Turns in direction should be on curves of such diameter as will allow the air to be diverted with the least friction. The general rule in handling air is that a curved duct should have an inside radius equal to three times its diameter. The water vapour present in air at ordinary pressures is most conveniently expressed in terms of percentage of relative humidity. Relative humidity is the ratio of the weight of water vapour actually present in a space to the weight the same space at the same temperature would hold if it were saturated. Since the weight of water vapour present at saturation for all temperatures here used is known, the actual weight present under different degrees of partial saturation is readily calculated from the relative humidity. Relative humidity is determined by means of two thermometers, one having its bulb dry and the other having its bulb closely covered by a silk or muslin gauze kept moist by distilled water. Tap water should not be used because the mineral deposits from it clog the wick, retard evaporation, and produce inaccurate readings. The wick must be kept clean and free from dirt and impurities. The two thermometers are either whirled rapidly in a sling or used as a hygrometer mounted on a panel with the wick dipping in a tube of water and the bulbs exposed to a rapid and direct current of air. The relative humidities corresponding to different wet‐ and dry‐bulb temperatures are ascertained from charts furnished by the instrument makers, or published in engineers' handbooks. As a general rule, the more rapidly the products have been dried the better their quality, provided that the drying temperatures used have not injured them. Some fruits and vegetables are more susceptible to heat injury than others, but all are injured by even short exposures to high temperatures. The duration of the exposure at any temperature is important, since injury can be caused by prolonged exposure at comparatively moderate temperatures. The rate of evaporation from a free water surface increases with the temperature and decreases with the increase of relative humidity of the air.

Starting at such a nutritional and health level as probably most people accept as their norm, it is now clearly possible (1) better to ensure a normally prompt development of the young, (2) to induce a higher level of adult vitality and accomplishment, and (3) materially to improve the duration as well as the quality of life, through the guidance of nutritional knowledge in the everyday choice and use of food. Three questions may have suggested themselves: (1) How conclusive are the data supporting such statements as those of the preceding paragraph?; (2) What are the grounds for confidence in the human application of the finding of laboratory animal experimentation in this field?; and (3) With all due reverence for individual human lives, will a longer‐lived population be an advantage? Each of these questions is worthy of a much fuller answer than the space here available permits; and could be answered with much ampler evidence and explanation, but for the present need of extreme condensation. Statistical analysis of the objective, numerically recorded data of laboratory‐controlled experiments shows, at all stages of the life cycle, nutritional improvements upon the initial norms with measured differences so manifold greater than their probable errors as to establish these findings with higher degrees of scientific certainty than probably attach to most of the unquestioned facts of physiology. The least‐expected of the new findings, namely, the extension of the normal adult life‐expectation, is objectively established with 100‐fold greater degree of statistical convincingness than the accepted canons of scientific criticism call for to justify the characterisation of such a finding is “undoubted.” The basal dietary of these experiments is representative of the food supplies upon which a large proportion of our people subsist; and the animal species chiefly used for the full‐life, successive‐generation experiments above mentioned is the rat, chosen primarily because of the many and close resemblances of the chemistry of the nutrition of that species and our own. The only known significant differences are with respect to ascorbic and nicotinic acids; and toward both of these the human species is much more responsive to the level of dietary intake than is the rat. Critical study reveals no reason to discount the above‐noted laboratory findings because of species difference; but, on the contrary, shows strong scientific evidence that the indications obtained from the experiments with rats are well within the probabilities of the nutritional improvement of human lives by intelligent use of our everyday foods. Such nutritional improvement results not only in longer life but also in the living of our lives upon a higher level of health and accomplishment throughout. The “extra time” is not added to the period of senility. It is inserted in the period of the prime, making this a longer fraction of the life cycle. Thus the nutritional improvement brings, to speak in human terms, both a larger number and a larger percentage of years of full accomplishment, and economic and social value, with a smaller proportion of years of dependency. Space does not permit the discussion here of the very real advantages, to the individual, to the world of industrial affairs, and to the nation, of an earlier attainment of full capacity and also a postponement of the onset of old age. How to extend the benefits of the newer knowledge of nutrition, as widely and as promptly as possible is both an economic and an educational problem. If space permitted, an abundance of statistical evidence could be assembled to show: (1) that, independently of educational opportunities, the families with better per capita purchasing power tend to provide themselves with nutritionally better food supplies; and (2) that also, among families exercising the same purchasing power in the same markets, some provide themselves with dietaries which are nutritionally excellent, others only good, and still others only fair. Much can be (and in many places is being) gained either by direct economic measures to increase the purchasing power of low‐income families whether by increase of money income or by making available to them larger supplies of protective foods at lower prices; or by widespread teaching of the nutritive values of foods and the influence of nutritional wellbeing upon health and earning‐power. Needless to say, the communities which have good use of both of these means of improvement may expect to reap the largest benefit. In an unbiased economic view everyone can see that there is opportunity for enormous benefit in using the new knowledge of nutritive values to guide the investment of the many billions of dollars that are annually spent in this country for food; and especially when the choice of food is now known to have greater and more far‐reaching effects upon health and earning power than has hitherto been supposed. But how often bias enters to cloud the economic view! Attempts to teach a more scientific investment of money in food are apt to meet a “vested interest” attitude of resentment from many purveyors of things which science cannot recommend for a higher place in consumers' budgets. And perhaps an even larger number of people “object on principle to,” or subconsciously react against, any attempt to teach discrimination of consumer demand, and any form of governmental paternalism or further extension of “government into business.” In addition to all the bias of an economic or political sort, tradition in itself retards change, especially in matters which come so closely home as does the family food supply. And in the domain of food, as one of the wisest students of nutrition has said, tradition tends to accumulate prejudices quite as often as truths. These and other causes tend somewhat unduly to caution in public teaching of the everyday use of the newer knowledge, which in terms of foods as bought and eaten is: Give fruits, vegetables, and milk in its various forms (including cheese, cream, and ice‐cream, if desired) a larger place in the dietary and food budget. This can be done without “cutting out,” and without too drastically “cutting down,” any other articles of food. As the Nestor of the new knowledge of nutrition has consistently taught: If we cat what we should, we can at the same time eat what we like. Another question sometimes arising is, How can we feel confident of the practical application of present nutritional knowledge when we admit its probable incompleteness by recommending further research? The present writer's answer is that some findings of such far‐reaching importance that their everyday application ought not to be postponed are conclusively established, and the practical advice above suggested is based upon these and is permanently valid. More elaborate and detailed dietary recommendations may well await the findings of such further researches as are briefly suggested below. Both further research and fuller application, neither delayed by waiting upon the other, should be strongly emphasised, especially in view of the present and impending situation. There should be prompt and wide dissemination of present knowledge at all teaching levels. And nothing is so stimulating to education as that research in the same field be actively productive at the same time. The best way to get a hearing, even for the findings now conclusively established, is to have some related new findings to tell. If made in large numbers, with great care, and on a comprehensive plan, further researches with natural foods as the experimental variables might be of great value. More accurate knowledge of the quantitative distribution of certain of the mineral elements and vitamins in foods can be sought with greater assurance of clear‐cut findings, and with certainty that these data will function both in the advancement of science and in the service of human welfare. There is also a field for much valuable research in the measurement of the nutritional availabilities of the mineral and other nutrients of the different articles and types of food, more especially by experimental methods which comply with the actual conditions of normal nutrition. With more precise knowledge of the nutritive values of a wider range of foods, it becomes increasingly practicable to ensure excellence of nutrition without sacrifice either of personal preferences in food selection or of the economic advantages which market fluctuations and seasonal conditions offer. Fortunately, most seasonal food crops are at their best when they are also at their cheapest. The fuller our knowledge of nutrition, the less we need depend upon diversification, but the better we are prepared to gratify a taste for it. The newer knowledge of nutrition is friendly to the fact that “eating has a great vogue as an amusement,” and several foods formerly regarded as luxuries are now seen to be good nutritional investments. The science of nutrition does not seek the sanctification of spinach: it looks with much more favour on many of the things that we find most fun in eating. The new knowledge helps in meeting the problems of both war‐time and peace‐time food supplies; and the findings of further research will doubtless help us all still further to harmonise our appetites and aspirations—to know how to eat both what we want and what will make us most efficient. Both for completeness of scientific explanation and to establish the boundaries of advantageous practical application of the findings, further research is needed even upon two of the three factors which, as mentioned in an earlier section, have already been studied more fully than others by our recently developed methods. As opportunity permits, similar studies should also be made of the long‐time effects of different levels of intake of each nutritionally essential amino acid, mineral element, and vitamin. Meanwhile, the factors which have already been found to be of outstanding importance in experiments upon the entire life cycle should now be studied by similar methods but with starting‐points at different ages so as to ascertain the influence of initial age upon the potentialities for nutritional improvement of the life history. In the planning of all such studies the world‐wide present interest in efficiency and preparedness will tend to give priority to those researches which bear most directly upon problems of the attainment of the fullest fitness, from what‐ever initial age, and the maintenance of optimal capacity for service. Fortunately, such advances of knowledge will service both science and the nation well, however long or short the war, and whatever its aftermath may be. Studies in nutritional rehabilitation deserve also a well‐considered place in the general programme for bringing the new knowledge into the service of all the people. Between the obvious cases of specific deficiency diseases and, on the other hand, the people whose physique and efficiency are within the zone of our present norm, too many even of our American people (and doubtless a higher proportion in most other countries) are handicapped, though we may not know exactly how and why. Many of these people can be rescued from individual and family frustration, and incalculably enhanced in economic and social value to the community and nation, by “enough of the right kinds of food”; and just what this means in more precise terms, how the greatest good can be accomplished with most promptness and efficiency, are problems within the scope of the present‐day methods of research in the chemistry of nutrition. Moreover, the same general type of research reveals good scientific probabilities of improving the chemistry of the internal environment, and thus enhancing the efficiency, of people who are already quite fortunately healthy and efficient.

Perhaps it should be said that optimal nutrition is an ultimate goal which science is not yet prepared to define descriptively in detail. Speaking operationally, we may say that recent research has established, fully and objectively, the principle of the nutritional improvability of the normal. The experimental evidence can, of course, be but sketchily presented in a review of this sort which attempts to summarise in so little space a scientific advance of undoubtedly far‐reaching significance. Under the necessity of extreme brevity, the writer trusts he will be pardoned for drawing illustrations chiefly from the work with which he is best acquainted. In experiments to determine what proportion of protective food suffices to balance a minimum proportion of wheat in the diet, it was found that a mixture of five‐sixths ground whole wheat and one‐sixth dried whole milk with table salt and distilled water (Diet A) was adequate in that it supported normal growth and health with successful reproduction and rearing of young, generation after generation. Yet when the proportion of milk was increased (Diet B) the average results were better. In the experiments just mentioned, an already‐adequate dietary and an already‐normal condition of nutritional wellbeing and health were improved by a more scientific adjustment of the relative quantities in which the staple articles of food were consumed. And in the comparison of the effects of these two diets the principle of the nutritional improvability of the normal was manifested measurably at every stage of the life cycle. Growth and development, adult vitality, and length of life all were normal on Diet A and all were better on Diet B. This research having been planned in terms of natural articles of food, the sole experimental variable was the quantitative proportion or ratio between the foods constituting the dietary. If, on the other hand, we turn to the consideration of individual chemical factors, we find that the single change in proportions of staple foods had the effect of enriching the dietary at four points: protein, calcium, riboflavin, and vitamin A. Subsequent experimentation was planned both in terms of these four chemical factors separately and in terms of diversification of the dietary by addition of natural foods of other types. Here it was found that enrichment of the original diet with protein alone or its diversification with other natural foods tended to a moderate increase in growth and adult size, but no distinct improvement in the life history. Clearly this indicates that the increased intake of protein played but little if any part in the nutritional improvement induced by Diet B over Diet A; and also strengthens the probability that the observed improvement is essentially explainable in terms of the factors we recognise, for if anything unknown had played an important rôle in this improvement, the diversification of the diet would probably have revealed some indication of it. Calcium, riboflavin, and vitamin A each is found to play a signicant part in the nutritional improvement of the already adequate diet and already normal health. With each of these three factors the level of intake giving best results in long‐term experiments is two or more times higher than the level of minimal adequacy. Some aspects of the respective rôles of these three factors are still subjects of further experimental investigation. It is not to be assumed that the wide margins of beneficial intake over actual need, found as just mentioned with calcium, riboflavin, and vitamin A, will apply to the other nutritionally essential mineral elements and vitamins. Each should be investigated independently in this respect; and with no presuppositions derived from the findings with calcium, riboflavin, and vitamin A, for these were not random samples, but were taken for rigorous experimental study because of the definite suggestions of earlier work. Meanwhile the above‐mentioned findings with the factors already comprehensively investigated afford a basis both for clarification of a fundamental chemical principle in nutrition, and for its practical application. One useful first‐approximation of nineteenth‐century science was that an organism may be expected to grow only as fast or as far as is consistent with the specific chemical composition of its kind; and another was that it is the fixité of the organism's internal environment which enables it to cope with new or changing external environments. It is surprising that these views continued to be held so rigidly for so long when at the same time there were developing physico‐chemical principles which call for a more flexible concept. In this light it seems clear that the so‐called steady states of the body are only relatively so: that one cannot introduce into the system different amounts and proportions of such active factors as we know some food constituents to be, without some resulting changes of concentration levels or of dynamic‐equilibrium points, or both. And now we have the objective evidence of well‐controlled, long‐term experimentation showing nutritional improvement of an already normal bodily condition in such manner as seems best expressed by saying that the chemical aspect of the body's internal environment has been modified for the better. Thus in accordance with physico‐chemical principles we now conceive the “normal level” of each nutritional factor to be not a single fixed level but a zone. Undoubtedly this zone is wider for some factors than for others, and probably also the most advantageous level is with some substances near the upper margins, and with other substances near the middle or the lower margins, of the respective normal zones. Thus while our bodies enjoy by virtue of their biological inheritance certain self‐regulatory processes of striking effectiveness, our minds are now finding, through chemical research, how these can be made still more effective by the scientific guidance of our nutritional intakes; by helpfully influencing our internal environments through good habits in our daily choice of food. Contemporary research in the chemistry of nutrition is here developing a fundamental and far‐reaching scientific concept which hitherto has hardly been apprehended because species have been regarded as more rigidly specific in their chemical composition, and the “steady states” of their internal environment have been regarded as more rigidly fixed, than they really are. The accepted generalisation that each life history is determined (1) by heredity and (2) by environment assigns all except hereditary factors to environment by definition. But as the result of nearly a century of scientific as well as popular habit of thought, the word “environment” actually connotes surroundings. Science exaggerated the extent and rigidity with which our internal chemistry is automatically regulated by our biological inheritance, to such an extent that there seemed nothing for us to do about it except to admire its wonders and stand ready to repair its occasional breakdowns. But now that we are finding ways to add conscious chemical control and improvement to the marvellous mechanism with which nature endows us, we can be not merely repair‐men to a biologically inherited bodily machine, but also architects of a higher health. It may help to make this newly‐opened opportunity clearer if, instead of the above‐mentioned two, we think and speak of three major determinants of our life‐histories: (1) heredity; (2) environment, in the familiar external sense of surroundings; and (3) the body's internal environment, which immediately environs and conditions the life process, and which in the course of the life cycle is much more significantly influenced than hitherto supposed by even the normal differences in what we take into our bodies as food. This responsiveness of our internal chemistry, and resulting degree or level of positive health, to our nutritional intake, usually becomes manifestly measurable only in cases of visible injury from nutritional deficiency, which, once apprehended, we seek to avoid; or in experimentation with laboratory animals whose natural life‐cycles are such as to permit of accurately controlled conditions and observations extending throughout entire lifetimes and successive generations. In the long‐controlled, laboratory‐bred colony of experimental animals used in large numbers for full‐life and successive‐generation feeding tests conducted with all the quantitatively meticulous care and precautions to which research workers in the exact sciences are trained, we now have an instrument and technique of investigation such as has not existed before. Much remains to be done in the new field of research thus opened; but work already completed shows clearly the possibility of nutritional improvements of already‐normal health, vitality and efficiency throughout our lives. Whatever we are individually born with, we can each do more for ourselves to influence our life histories in the direction of our aspirations than science has hitherto thought.

Generally speaking a “new” loaf is demanded and the baker who cannot deliver “new” loaves loses trade. But what is a “new” loaf? From the point of view of the chemist this question has formed the subject of innumerable investigations. A definition of a “new” loaf demands an understanding of “staleness” and the staling of bakery products is a subject of great complexity. The old idea was that it was entirely a question of the “drying out” of the bread, but cereal chemistry has proved that such a solution, namely the prevention of “drying out,” is only of partial efficacy; in fact “staleness” is caused by a change in the starch of the flour which is inherent in it and cannot be prevented by precautions which maintain the moisture content at a certain figure. The investigation of this type of staling has occupied the attention of many famous chemists, but the full explanation has not yet been obtained. Mass production has demanded many studies in that aspect of science known as “physical chemistry.” An example can be found in the preparation of certain sauces. Those of you who have made mayonnaise sauce know that to beat the olive oil into the mixture is fraught with difficulties. By means of the fork, used as a beater, the oil is distributed in very small particles through the mass of liquid, so that every globule of oil is separated from every other one. If the action docs not proceed properly the system breaks down and the mayonnaise “turns” and is spoiled. The manufacturer has to prevent this “turning,” not in a few pints but in hundreds of gallons. It is the chemist who has enabled him to do this and to manufacture with success those scores of salad‐dressings which are so delectable and the purchase of which relieves the housewife of so many hours of work and so much arm‐ache. An example of some interest is concerned with smoked salmon, which normally is a very variable product, whether it be the highly salted variety of the northern climes or the much less salted kind which has found favour in this country. The production of a lightly salted product is far more difficult than the more salted variety because much smaller changes in salt content become more noticeable. These small differences are so obvious to the confirmed smoked salmon eater that he detects not only the differences between one grade and another, but also the differences of salt content that occur in different parts of the same side of fish. It has fallen to the chemist so to change the methods of production of the lightly flavoured variety that the distribution of salt through the fish is even and the flavour therefore constant. This study of smoked salmon is only an example of the very big problem of standardisation, standardisation demanded by the consumer—and it follows that the big manufacturer must produce goods of standard flavour and appearance. Science steps in and gives the manufacturer those controls which enable him to produce, day in and day out, that standard range of article, whether it be ice‐cream or toad‐in‐the‐hole, Worcester sauce or cheese cakes, roast beef or jelly crystals. Modern science has introduced a new factor into our conception of what food should be. In the past it was only necessary to ensure that food should be “pure and wholesome,” by which was meant—in general terms—digestible and without any harmful constituents, be they natural or adventitious, bacterial or otherwise. So long as food complied with this broad definition everyone was satisfied. But biochemists and physiologists have demonstrated the importance of other factors, salts and vitamins, and it is necessary to consider the new situation thus created because it may be that the treatment of food to retain those substances may make it necessary to change preconceived notions. It may be that “palatability” may be affected, palatability which includes taste and appearance and odour. The whole subject is so complicated and, notwithstanding the enormous amount of work carried out, so little understood that no one as yet can be dogmatic, no one can state what are the optimum amounts of vitamins required by ordinary persons to keep them in good health. Having, however, decided the amount required, are we to try to preserve such quantities as occur naturally, or are we to fortify the food which we cat by added synthetic or even by purified natural vitamins? A further important consideration is whether the degree of maturity of, say, fruit in relation to maximum vitamin content coincides with optimum palatabilty. Certain it is that information gradually being accumulated on the importance—in many cases vital importance—of the minor constituents of foodstuffs leads to the conclusion that, to ensure the presence of all valuable minor constituents—be they known or unknown—the foodstuffs must, as articles of diet, be ingested almost in their entirety. This is probably an extreme view, for, in many cases, the result would be a product of reduced palatability or appearance, or, what is probably more important, “different,” and people do not like their food to be abnormal, i.e., to differ from their preconceived notion of what it should be. Nevertheless an “improvement” in the method of production, put into practice by the food manufacturer with the best intentions, may possibly result in a lowering of the dietetic value of the food, as, for example, by mechanical removal of an important part (the classical example being polished rice), by heat treatment, by oxidation or by materials added during cooking. The minor metallic constituents of food are gradually being revealed in their true importance. Copper, zinc, and iron are now known to be of importance. It is probable that every baby is born poor in calcium but rich in iron; milk, the natural food of the infant, is rich in calcium. It is only in the last few years that it has been shown that green vegetables as usually cooked are of very little real value. Cooking green vegetables in water containing sodium carbonate results in the almost complete destruction of the Vitamin C, and the discarding of the water removes the extracted salts. A green product certainly results but of greatly reduced nutritional value. On the other hand, it would appear that little destruction of vitamin activity takes place when the canning of vegetables or fruits is properly controlled. Sherman has said that attention to mineral salts and vitamins will lead to “buoyant” as distinguished from merely “passable” health. It is obvious that education of the public is essential if an intelligent use is to be made of the knowledge being gained by chemists and allied scientists. It is a most important fact that methods are being developed to assay foods for vitamins by chemical means. Biological feeding tests are obviously unsuitable for control purposes but, as the chemical identity of the vitamins becomes more clarified, chemical tests will become available for their determination. It is obviously the duty of the medical services of the country to guide the public as far as is possible on questions of nutrition. When such guidance becomes effective, the food producer will not be slow to see that his goods are up to the standard necessary, adding one more burden to the already loaded back of the chemist concerned with food production.

Heat treatment, in view of later knowledge, is seen to have other effects than to destroy or lower the vitality of micro‐organisms initially present; there are the more obvious changes of flavour and of consistency brought about by the partial cooking, but there are also the possible lowering of the vitamin potency and the still more subtle changes in the salts which may, after heat treatment, be rendered less available than in the raw product. The importance of these considerations cannot be too much stressed when it is remembered that heat treatment is, generally speaking, an inherent stage in the process of canning. It is the heat treatment which preserves the goods, the sealing of the can being merely a means of prevent re‐contamination. The chemist, no less than the physiologist, has been much concerned with the changes in foods caused by heat treatment as a method of preservation, and, as a result of his investigation, there is now a better understanding of the changes which take place, with a consequent improvement in the methods of processing. For a number of years, however, this country, in common with many others, has relied, in so far as its supplies of meat are concerned, on products preserved by “cold,” and the freezing of beef, the chilling of mutton, have made available to us the cattle of the Argentine and the sheep of New Zealand. Initially the processes employed were crude, the post‐mortem changes were imperfectly understood, conditions of storage, before, during and after shipment, were haphazard, and the methods of defrosting far from scientific. How far the methods have advanced, and to what extent the scientist has been concerned in the elucidation of the many problems, will be realised from the reports of the Food Investigation Board. It is not suggested that all the advance is due to the work of the Low Temperature Station a Cambridge—much has been done in other countries‐but the investigations carried out by the scientists a this station have been fundamental. Food producers in America were the first to realise the importance of the latest development in freezing, the advent of the “ Quick Freezing Processes ” marking a distinct advance in technique. When cellular tissue is normally frozen and subsequently defrosted, rupture of the cells may have occurred and the structure of the substance consequently partially broken down. When, however, the tissue is quickly brought down to a very low temperature, it is found that in many cases this breakdown in tissue does not take place. These principles have been applied to commercial installations, and fish, meat, fruit and vegetables so treated show on defrosting remarkably little change in character. Preservation by desiccation is a method employed for certain materials with great success. Sun‐drying of fruits (sultanas and dates, to quote but two) and the sun‐drying of cereal products such as macaroni is still practised. An important industry concerned with the drying of milk has developed in most milk‐producing countries, whilst dried eggs and dried egg‐albumin form important items of commerce. It is obvious that the object of concentrating such substances as fruit juices, milk and vegetables and animal liquid extracts is ideally to reduce the water content and obtain a product which, when the water is ultimately restored, gives a solution or material having the original taste, aroma and food value. The effect of heat is often, however, to change these characteristics, and although by the use of a vacuum the temperature to which the substance is submitted is lowered, changes still take place, and much of the aroma depending on volatile constituents is lost. To a very great extent this has been overcome by a method of desiccation which is essentially partial freezing, a method which has not yet received much publicity as it has only lately emerged from the experimental stage. The practical application of this principle is due to Dr. G. A. Krause, of Munich, who has invented and designed a dual process of concentration. In this process the liquid is first concentrated by freezing out water as ice, which is removed by mechanical separation in a centrifuge. By ingenious mechanical and regenerative devices this process has been made extremely efficient, the losses being only 1–2 per cent. of the original juice, although the efficiency is not maintained when the solids‐content of the product has been raised to 40–50 per cent. This liquid is then further concentrated by evaporation at a low temperature, about 10°–15° C. The differential evaporation of water as compared with the aromatic flavour constituents occurs because the removal of water as vapour at this temperature depends solely on the rate of diffusion of the molecules into the gas space. As water has a small molecule compared with the large molecules of the esters, ethers and alcohols of the flavouring substances, it escapes more readily ; the conditions of evaporation as given in the patent are all designed to aid this escape. A reduction in pressure may be used to speed up the process without interfering with the differential diffusion, and the provision of an atmosphere of small molecules (e.g., hydrogen) also has the same effect. A large surface for the evaporation is made by spreading the liquid as a thin continuously renewed film. The condenser is situated very near the evaporating liquid to remove the water molecules quickly (a distance of 3 cm. is the maximum diffusion path). The atmosphere may be circulated or disturbed to hasten the diffusion and, most ingenious of all, it may be blown towards the evaporating liquid when, if a velocity is used just greater than that of the heavy molecules leaving a liquid surface, the loss of flavour may be entirely eliminated while the rate of water evaporation is only reduced by 10 per cent. By these means a concentrate containing as much as 65 per cent. solids and capable of storage without deterioration at ordinary temperatures may be prepared, and 80 per cent. of the original vitamins retained. The use of refrigeration in the preservation of food has necessitated the use of refrigerated transport to complete the links between producer, manufacturer, retailer and customer. The variety of commodities and the different conditions they need create varying demands on the methods of insulating and refrigerating transport vehicles. The British railways have 4,000 refrigerated railway vans, and such vans, containing perishable produce, came regularly to England from Austria and Italy by way of the train ferries. These vans are designed for fairly high temperatures, 35–40° F., and long hauls, and use ice as a refrigerant. At the other end of the scale is the road vehicle, which may have a temperature as low as 0° F., but is only on its journey about 12 hours. It is in these road vehicles that the greatest advances have been made, for conditions in England do not justify the railways in expenditure on elaborate equipment. The early road vehicles were insulated boxes on a lorry chassis and were refrigerated by ice and salt, which was “messy” and caused bad corrosion of the chassis. The introduction of an eutectic solution, virtually a mixture of a freezing salt and water in a definite proportion, which was frozen as a whole in a sealed tank, was made some few years ago. This removed the “messiness,” conserved the salt and produced greater efficiency and a more stable temperature.

The Milk and Dairies Bill introduced by Mr. SAMUEL aims at securing better inspection of dairies, including all premises in which milk is obtained, stored, or sold, such as cowsheds, milk depots, and milk shops. It also aims at the tracing of impure milk and the prevention of its infection, as well as the elimination of cows yielding tuberculous milk.

Among the wine producing countries of Europe, Italy takes the second place after France. And it is not at all a bad second, as the figures of the average wine production of the vine‐growing countries of Europe and the Mediterranean Basin for the ten years prior to the outbreak of war, i.e., from 1929 to 1939, will clearly demonstrate. They were: France, 58,624,000 hecto‐litres; Italy, 39,189,000 hectolitres; Spain, 19,290,000 hectolitres; Algeria, 17,309,000 hectolitres ; Roumania 8,281,000 hectolitres; and Portugal, 7,289,000 hecto‐litres. The six countries then produce an average of roughly 150,000,000 hectolitres of wine annually, or approximately 80 per cent. of the total world production, which is in the neighbourhood of 187,000,000 hectolitres. Thus Italy's output stands for just over one‐quarter of the European production and one‐fifth of the world crop. From her grape harvest, Italy produces each year round about 6,000,000 hectolitres of wine of quality and 1,200,000 hectolitres of Vermouths, Marsala and other special wines. Then roughly half a million hectolitres are devoted to the making of vinegar and another 4,000,000 go to the production of second‐class alcohol. The remainder of the crop is converted into the ordinary wines which until recently were mainly consumed by the Army and the civil population. But while quantitatively Italy takes second place among the European wine producers, actually, from the point of view of the yield per square kilometre of vines planted, she ranks first. That will be obvious when it is pointed out that France obtains a crop of approximately 114 hectolitres for every square French mile or kilometre, while the Italian figure for the same area is 132 hectolitres. No other country equals this.