Atherton Seidell of the public health service, in the current number of the Journal of Industrial and Engineering Chemistry. These elusive substances have been found necessary not only as dietary factors but even for the prolongation of life. Their exact nature, however, still remains a mystery, though much has been discovered concerning their effect on the human system and the general benefits conferred by them. For instance, experiments have proved that animals can live indefinitely on a diet of milk alone. But supply all the constituents of milk separately. — proteins, carbohydrates, fats and salts, in fact, all the known food elements—and the animal wastes away and finally dies.
Several theories are held in regard to this problem. Some scientists in an hour at the clinic to classify vitamines as structural compounds of living tissues, which function along the same lines as the other tissues. Others relegate them to the "catalysts," those strange substances which have been aptly defined as "chemical parsons," as they accomplish the chemical union of varipus substances without being themselves affected. Many think that they are derived originally from plants, and one well-known scientist states that they are always present in natural foodstuffs instinctively consumed by men and animals.
Three Types of Vitamine.
At the present time, three types of vitamine are known to exist; The water-soluble variety, found in milk, yeast, and other substances; the fat soluble ones, which are present in butter and egg yolks; and a third class, designated as "antiscorbutic," which is found in a number of fresh   Vegetables and fruits and also in the outside husk of rice. Lack of these necessary food constituents results in various ills—scurvy, beri-beri, and other diseases. 