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A VERY large amount of nonsense is written on the subject of vitamins, and some good purpose may be served by attempting to summarize what is known at the moment of writing, and may be out of date when this article is read. For a long time in the past it had been understood that scurvy was due to a special type of monotonous diet, and could be cured by small amounts of certain fruits and vegetables, or larger quantities of fresh meat. Later the same was proved for beri-beri and suspected for rickets and other diseases. Meanwhile the problem of the ideal diet had been largely solved in the nineteenth century. It was shown that one of the first necessities was a sufficient fuel value in the food. When burnt it must be able to provide the energy needed by the body. But only a few substances, namely, carbohydrates, fats, and proteins, will serve as energy sources, and not too much must be fat. A certain minimum of proteins, which must be of the right quality, is needed for repairs of the tissues. Elements like iron and calcium must also be present in small amounts.

In the early twentieth century the problem was attacked from two points of view. First of all, a number of workers dealt with the question of what had to be added to an otherwise complete diet in order to prevent a given deficiency disease. This may be called the analytical method. The converse or synthetic method, of which Hopkins was the most successful exponent, asked the more ambitious question, ‘Can we make a complete diet out of substances of known chemical composition, and, if not, what must we add to it to make it satisfactory?’ These lines of research have now converged. Besides the discovery of the vitamins they have led, among other things, to a knowledge of what chemical properties in a protein are needed to make it a satisfactory constituent of a diet, and to the proof that most cases of goitre are due to iodine deficiency, while traces of zinc are almost certainly necessary in the diet.

It now seems that besides proteins, carbohydrates, fats and inorganic substances, at least five rather complex organic bodies are needed. Hopkins called them accessory food factors. Funk, who had obtained a preparation containing a good deal of one of them and believed that he had got it pure, called it vitamine; and this name not only caught on, but was applied to the other accessory factors.

The general method of research is as follows. Two groups of very similar animals, usually rats, are fed on diets which differ in only one particular, say, the addition to one of them of a little killed yeast; and the difference between the two groups is observed. The group on the adequate diet may grow faster than the others, form better bones, have more young, or what not. It is rarely necessary to push the experiment so far as to lead to the death of the group on a deficient diet, and they often look quite healthy and behave normally. Indeed, since so many pet rats receive very unsatisfactory food the most striking thing to a casual observer may be the robust health of the animals on a really adequate diet. When the original experiment has been repeated and confirmed, and the exact amount of the added substance needed per rat per day has been determined, one proceeds to hunt down its essential constituent. ‘Can it be replaced by its ashes?’ we first ask, and when the answer is ‘No’ we are sure that we are not concerned with an inorganic substance, such as iron or iodine. ‘Is it soluble?’ The answer so far has always been ‘Yes,’ if we choose the right solvent; in certain cases, water, in others, ether or some other liquid which readily takes up oily substances.

We now try to purify it. For example, the substance in cod-liver oil which cures rickets is left behind when 99 per cent. or more of the oil is converted into soap and glycerine by heating it with alkali. We can thus obtain a preparation many hundred times richer in the antirachitic substance than was the original cod-liver oil. Sometimes the purification may show that where we thought we were dealing with a single substance we have really got two. For example, several workers obtained liquids very rich in the substance which prevents the convulsive seizures due to polyneuritis which occur in its absence. The cruder preparations of this substance always contain a substance (vitamin B₂) whose absence causes loss of weight. But the most active antineuritic preparations do not prevent this loss, so it is concluded that the antineuritic vitamin is not vitamin B₂. From such experiments we arrive at the following provisional list of vitamins. The lettering of A, B, and C is McCollum’s, and is generally agreed on. That of the remainder is still under discussion.

A is an oily substance found in many natural fats and oils, cod-liver oil being particularly rich in it. Its absence leads to failure of growth in the young, and in both young and old to a tendency to inflammation of the eyes, and increased liability to various diseases. Night blindness is often an early symptom of its absence. It is slowly destroyed by cooking.

Vitamin B₂ is found in a variety of foods, especially in certain portions of wheat and rice grains. Its absence causes failure of growth or loss of weight. Pellagra, a disease common in populations living mainly on maize, is probably due to an inadequate supply of it. It is soluble in water.

C is widely distributed, but certain fresh vegetables and fruit are particularly rich in it. It is soluble in water, and rather easily oxidized, hence the emphasis on freshness. Its absence causes scurvy, but a good many infantile troubles are also due to a shortage of it.

D is a waxy substance, long confused with A, and associated with it in nature. Both, for example, are found in cod-liver oil. We can make it in our own bodies, provided that we get enough ultra-violet ‘light’ on our skins.

As, however, not only clothes, hats, and fogs, but even glass windows screen us from this component of the sun’s rays, it is safer to be sure that our diet contains the vitamin. Children and young animals kept in inadequate light without it generally develop rickets, but may not do so if the amounts and proportions of calcium and phosphorus, the bone-forming elements, in the diet are kept exactly right. Vitamin D is formed by the action of ultra-violet radiation on ergosterol, a substance of known composition, and is the only vitamin yet obtained in a fairly pure state. Apparently this is the only dietary factor that is made by radiation, for no amount of sunlight will make up for the absence of any of the others.

E is also of an oily character, and is present in various foods, particularly wheat bran. In its absence rats grow up and live healthily, but they cannot reproduce. They can neither become fathers nor mothers. Such at least is the statement of its American discoverers, Evans, Bishop, Burr, and Sure, and their work has now been repeated in this country; but at least one observer in the United States has obtained a contrary result. The existence of this vitamin cannot therefore be regarded as absolutely proved.

The antineuritic substance which accompanies B₂, and has very similar properties to it, is now generally called B₁. In the absence of B₁ and B₂ the very serious tropical disease of beri-beri develops in man, and the ‘war dropsy’ of Central Europe was probably due to the same cause, but until these substances have been more satisfactorily separated it is not quite clear which of the two is the main preventative of any given complaint. There is further evidence which makes it quite likely that the above list is not exhaustive.

It is customary to conclude an article on this subject with an admonition to consume more fruit, fresh vegetables, or raw milk. The custom would be laudable if vitamin deficiency were the only fault to be found with our diets. But, as a matter of fact, about half the human race at the present moment is suffering from partial starvation, and the first requisite for them is to eat more of the cheapest food they can get, vitamins or no vitamins. And among those who read this article I suspect that for every one who is seriously the worse for vitamin deficiency there is another suffering from constipation due to a too digestible diet, which leaves no residue of husks and fibres, and three or four victims of bacteria and worms which they have absorbed with their food.

To take a simple example, I would sooner have my child run the risk of rickets or infantile scurvy from over-boiled milk than of tuberculosis from drinking it raw. I refer here to British milk—American is less tuberculous. Again, raw vegetables, though full of vitamin C, are an admirable vehicle for the typhoid bacillus, which is commoner in the United States than England. And they are so liable to contamination with the eggs of parasitic worms that the Strasbourg International Congress on cancer, impressed by the proof that worms may produce that disease, issued a perhaps unduly solemn warning against the consumption of salad. While, therefore, we cannot neglect the teachings of bio-chemistry in our choice of diet, we shall do ourselves no good if in the attempt to be up to date we neglect the lessons to be learnt from parasitology and bacteriology.

But if we are sure that our food is uncontaminated, and that there is enough of it, an adequate supply of vitamins is the next consideration. And nowhere is this consideration more urgent than in the case of infants, who can ask for more, but not for better, food.