VITAMINS. Substances of unknown composition normally present in certain foodstuffs in minute quantities, the absence of which from the diet leads to well defined morbid states.
Accessory Factors and Growth.—The realization of the existence of vitamins grew gradually out of numerous attempts, made at various times, to feed animals on diets of known compo sition, as free as possible from all admixture (1881, Lunin). Much later it was found in England (1906-12, Hopkins) that under these conditions the animals lost weight and died but that if a relatively small amount of milk were included in the diet the animals flourished and increased in weight.
Simultaneously in Germany (1909-12, Stepp) somewhat simi lar observations were made and Stepp, like Hopkins and Lunin, concluded that something more was necessary for life than the amounts of pure carbohydrates, proteins and fats needed to sat isfy the animals' requirements of energy and of material for new growth and the replacement of waste tissue. These facts were repeatedly confirmed in England and America, but the explana tion was hard to find. A partial solution of the problem was afforded by the discovery in America (1913, McCollum and Davis) that on certain diets, themselves inadequate, growth could be induced in rats by the incorporation in the diet of the substances extracted by ether from yolk of egg or butter. On other diets however, this addition was found to be ineffective and a more complete comprehension of the conditions was only attained after the discovery (1915, McCollum and Davis) that not one but two "accessory" substances were required in addition to pure carbohydrates, proteins, fats and salts. For convenience these "accessory factors" were termed Fat-soluble A and Water soluble B.
detailed laboratory study of the disease, which was soon rewarded by the discovery that it followed on the absence from the bird's diet of a substance present on the "silverskin" or pericarp of the rice grain (which is removed in the process of milling and polishing) and could be cured when this, or an extract of it made with water, was administered. The experimental method thus established enabled the occurrence of this curative substance in other materials to be studied both qualitatively and quanti tatively, as well as the effect upon it of varying conditions such as temperature and oxidation.
A precisely similar course of events took place with regard to scurvy (q.v.). It was found in Norway (1907 Hoist and Frohlich) that scurvy could be induced in guinea-pigs by remov ing the greenstuff from the ordinary feed of grain and cabbage leaves and by giving a diet consisting of grain and water only. As in the case of beriberi rapid progress followed experimental study of the disease and it was soon established that scurvy fol lowed on the absence from the diet of a constituent present in fresh cabbage and in many fruit juices. By the use of guinea pigs (and later of monkeys, which are also susceptible to the disease) it became possible to study the distribution of the pre ventive substance both qualitatively and quantitatively in food materials.
The closeness of the analogy between the "accessory factors" necessary for growth and the unknown substances which were essential for the cure or prevention of beriberi and scurvy led to the inclusion of all these in one class, the vitamins (Funk 1912).
Although much has been added to our knowledge since the original classification of the vitamins as water-soluble and f at soluble they may still be conveniently divided into these two groups, the former comprising vitamins and which have both been found to be present in the original "water-soluble B," together with vitamin C, the antiscorbutic vitamin, and the latter vitamins A and D, corresponding with the original "fat-soluble A," and vitamin E, the anti-sterility vitamin.