Vitamin A has been found to occur both as such and in the form of several precursors, and rather than try to coin one word to cover several substances we continue to use the alphabetical designation, with or without mention of precursors, or we say vitamin A value. In addition to its many other functions in our bodies, vitamin A has been found to be immediately essential to vision, a fact effectively used in the introductory summary of the Federal volume “Food and Life.” Vitamin B has been differentiated into thiamin, riboflavin, nicotinic acid, pantothenic acid, and pyridoxine, all now structurally identified, while still other possibilities are under investigation. Thiamin prevents and cures some of the most prevalent of the nerve diseases both of the Orient and of our Western World; and as it aids a fundamental intermediate step in the nutritional chemistry of all of our organs and tissues, it is proving helpful in a surprising diversity of ills. Nicotinic acid—a substance not nutritionally related to nicotine, and until lately little more than a laboratory curiosity— has been found dramatically potent in the cure of the conspicuous inflammation of the skin (and tongue) which gives the name to the disease pellagra which has been extremely prevalent in our Southern States; and which may perhaps afflict other regions and other countries to a larger extent than is recognised. Few discoveries could be more striking than that of the potency of this simple and inexpensive substance in the prevention and cure of such a scourge as pellagra. Yet it remains to be said that when the typical pellagrin has been cured of his pellagra by means of nicotinic acid alone, he needs something more to make him a fully healthy man. The previous diet of the poor pellagrin has usually contained so little of foods other than grain products, fats and sweets as to make his bodily condition that of a multiple nutritional deficiency instead of a “single” or “simple” one. Clinical treatment with the pure vitamins, separately and in combination, shows that the typical pellagrin probably needs riboflavin almost as much as he needs nicotinic acid, and often needs thiamin also, while in only less degree his “one‐sided” food supply is likely to have involved other shortages as well as these three. Good diet cures all of these deficiencies at once, and renders unnecessary the further investigation of the frequency in the pellagrous population of shortages other than those of nicotinic acid, riboflavin, and thiamin. It is believed that if these three vitamins were regularly and adequately added to white flour and to the corresponding products of corn, illness would be reduced and the efficiency of our people improved; while there would still be a higher goal ahead to be reached through better understanding and appreciation of what constitutes a well balanced dietary or food supply, and what it can do for one's health and efficiency. In the case of the antiscorbutic vitamin the new world has done much to repay its debt to Europe. The old world got the potato from the new, and with year‐round availability of potatoes scurvy became relatively rare. Also, it was an American physician who first clearly set forth the view that the antiscorbutic property of “fresh” food is due to a definite substance; and an American chemist who first identified this substance now called interchangeably ascorbic acid or vitamin C. Another of this rapid series of dis‐coveries was the finding of a vitamin since differentiated into several, the vitamins D, preventive of rickets which had recently been called the most prevalent of all diseases outside of the tropics. Any one of such discoveries of nutritional means for the cure and prevention of previously baffling diseases might alone have made this generation memorable in the history of the medical sciences and of human progress. Not only did these discoveries open men's eyes to a broader and clearer view of their ills: that not every disease is to be explained in terms of the presence of something injurious, because several are now seen to be due (instead) to a lack or shortage of something nutritionally essential. In addition, these discoveries led to a further and more constructive advance. Even while the chemical identification of the earlier‐discovered of the vitamins was still in progress, means of measuring them through their effects had been worked out and much active and fruitful research was in progress upon such quantitative problems as, In what relative abundance do these substances occur in different types of foods and elsewhere in nature? How much is required in nutrition under different conditions?, and How liberal a nutritional intake of each yields best results in the long view which considers the whole lifetime and successive generations? Laboratory research upon problems of amounts or proportions of nutritional intakes has also gained much through the clear recognition of the scientific value of the use of two kinds of experimental variable: (1) the individual chemical factor; and (2) the actual article of food as produced by nature or agriculture and consumed in everyday life. The chairman of the League of Nations' mixed committee on nutrition reduced the problem of food supply to its simplest terms when he said that what is needed is, “Not only enough food but also enough of the right kinds of food.” In the nature of things the “protective” foods must usually be more expensive, calorie‐for‐calorie, than the more abundant “fuel” foods such as the chief grain crops. Thus for most low‐income families at all times, and for greater proportions of the people during food shortages such as accompanied and followed the first World War, and now threatens the world again, a persistently outstanding problem is, What proportion of protective food is needed so to “balance” a dietary or food supply as to permit the full development and exercise of the innate capacities of those subsisting upon it? Twenty years of experimentation in the field that this question suggests, with large numbers of laboratory animals continued throughout the entire lifetimes of successive generations under the standards of control characteristic of research in the exact sciences, have brought accurately measured objective evidence that there is an important distinction between the merely adequate and the optimal in nutrition; and that the difference between the minimal‐adequate and the optimal levels is much greater for some nutritional factors than for others.
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