But what is the function of these vitamines? If fats and carbohydrates supply the fuel, and proteins the material for tissue supply, and mineral salts are needed for bone construction, etc., just what do the vitamines supply? We do not know. Some, such as Professor Gies, are of opinion that they supply the body with certain necessary chemical units which the body is unable to manufacture. Others - Professor Hopkins, for example, - regard these vitamines in the light of stimulators, in that they exert a stimulating influence upon the various activities of the body. But all this is intelligent guesswork and nothing more.

Now we must proceed to develop the whole subject of vitamines in such detail, and yet in so nontechnical a way, as to convince the reader that, though no one has ever set eyes on a vitamine, vitamines are real things and quite indispensable as part of our dietary. We have been eating them ever since man and things that have life appeared on this planet; but we were ignorant of the fact. Like certain amino-acids (in proteins) which serve as indispensable units in the building and repair of protoplasm, and which always formed a part of our diet even long before we were aware that such substances as amino-acids existed, so with these vitamines: we have used them always, but we have discovered them only within the last few years.

Stepp's Experiments, In 1909, some three years after Hopkins had begun the earliest of his experiments, Stepp, a German, turned his attention to the importance of the fat moiety in diets. He was particularly interested in certain very peculiar substances that are present in every cell and whose function is to this day very obscure: the lipoids. They are always very closely associated with the fats in food and living tissues. Wherever fats are, there are lipoids too; and the very solvents that remove fats remove most of the lipoids.

Stepp found that rats fed with bread made with milk throve and in time begot young that in turn developed quite normally. When the bread was first extracted with a mixture of alcohol and ether and the residue offered as food to the rats, the animals declined rapidly. Upon the addition of the alcohol-ether extract to the residue, the animals again began to gain in weight. Evidently the mixture of alcohol and ether extracted "something" - or more than one thing - which is a necessary constituent of food.

Since this ether-alcohol extraction may sound a little vague, let us turn to a simple experiment that may help to make this clear. In a dish we mix some sugar, sand and charcoal together. We next pour some water into this mixture and stir. The chemist will tell you that neither the charcoal nor the sand dissolves in the water, and your own experience will corroborate such an assertion; on the other hand, the chemist knows and you know that sugar does dissolve in water. The effect then of adding water to the mixture of sugar, sand and charcoal is to extract the sugar from the mixture. And just as water extracts sugar from a mixture, so will alcohol, and particularly ether, or both ether and alcohol together, extract fats and lipoids from a mixture such as food.

When therefore Stepp found that bread made with milk was a wholesome food, whereas bread after extraction with alcohol and ether was not, he concluded that the cause of such a deficient food was due to the absence of fat, or lipoid, or both. He ruled out the protein because that is as little dissolved by alcohol and ether as is sand by water. He ruled out fat because the addition of butter fat to the residue left after the alcohol-ether extraction, failed to improve the condition of the rats. Neither did the addition of a variety of mineral salts help in any way. Aside from fat, the only other possible constituents in this alcohol-ether extract - in proportions at all appreciable - were the ill-defined group of substances known as the lipoids; and Stepp expressed the opinion that the absence from the diet of one or more of these lipoids gave rise to nutritive decline.

Without necessarily agreeing with Stepp's conclusion regarding the efficacy of lipoids, his experiments did show quite clearly that something other than fat, protein, carbohydrate and mineral salts is necessary in an adequate diet; and in this respect Stepp's conclusions were in accord with those of Hopkins.

Drs. Mccollum, Osborne And Mendel

Now come a few significant observations by Drs. McCollum, Osborne and Mendel. They found that an unwholesome diet with isolated foodstuffs in which fat was represented in the shape of lard, could be converted into a perfectly wholesome one by merely replacing the lard with butter fat. Lard, obtained from swine, is as much of a fat as butter fat or olive oil, or any other of the several varieties of fats and oils on the market. The differences among the fats are largely due to differences in quantity of the three fatty acids they usually contain. The differences can never be as profound as those between proteins, formed as the latter are from eighteen different amino-acids.

When, therefore, our investigators found the substitution of lard for butter fat to produce loss of weight and general decline in rats, they attributed the deficiency of lard not to the fat itself, but to a something accompanying the butter fat and not the lard.

This something, this vitamine let us call it, was being tracked to its birthplace. Hopkins' experiment had shown that milk contains a vitamine; but milk is a pretty complex fluid. Is the vitamine distributed evenly throughout the liquid, or is it confined to one or more constituents of the milk?

Stepp's work pointed rather vaguely to the fat; but our three American investigators converted this vagueness into reasonable certainty.