~Function of "Fat Soluble A."~--All investigators agree that the "A" vitamine is an essential factor in the growth of young tissue, and the repair of mature tissues. McCollum claims that this vitamine is likewise a factor in the prevention of the eye disease known as xerophthalmia, and other scientists also hold this opinion. Eddy states that a diet lacking in the "A" vitamine will, in the majority of cases, result in stunted growth and the development of the eye disease, and that the appearance of the latter may be taken as a sure indication of the absence or deficiency of this vitamine.
The following diagram shows the effect of adding fat soluble "A" to the diet which was adequate in other respects. This chart represents the growth curve of young rats.[12]
230 +----------+----------+ | | | | | | | | | | | | | | | 190 +----------+---------/+ | | / | | | / | | | / | | | / | | | / | 150 +----------+---/------+ | | / | | With | / | | "Fat |/ | | Soluble / | | A" /| | 110 +--------/-+----------+ | / | | | / | | | / | | | / | | | / | | 70 +--/-------+----------+ | / | | |/ Without "Fat Soluble A" |----------|----------| | | | | | | 30 +----------+----------+ 0 1 2
Figure showing the effect upon growth of adding "fat soluble A" to a diet adequate in all other respects. Courtesy of Dr. E. V. McCollum.
Mellanby of England believes the "A" vitamine to be a factor in the prevention of rickets. Scientists of America have recently investigated this disease, and Dr. Hess (New York) has found cod liver oil to be a remedy for it. Cod liver oil is known to be rich in "Fat soluble A," but whether the cure of rickets is due to the presence of this vitamine in the oil, or to a possible fourth vitamine, is still undetermined.
~Effect of Heat on the "A" Vitamine.~--Heat, as applied in the ordinary methods of cooking, is not believed to exert a great deal of destruction upon the "A" type of vitamine; but hydrogenation, the process used in the hardening of certain fats in the manufacture of lard substitutes, is said to destroy it completely.
~"Water Soluble B."~--The second vitamine discovered in milk and believed to be identical with the Funk vitamine is more widely distributed than the "A" vitamine. For this reason it is not so likely to be deficient in the diet as is found to be the case with the "A." A glance at the table shows that the best sources outside of yeast are the seeds of plants and the milk and eggs of animals. In beans and peas the "B" vitamine is distributed throughout the entire seed, but in the cereal grains it is found chiefly in the embryo. As a result, bread made from fine white flour or meal is much more apt to be deficient in vitamine of the "B" type than that which is made from the whole grain; the same is true of rice and other cereals. Spinach, potatoes, carrots and turnips show an appreciable amount of the vitamine, but beets are known to be extremely poor in it. Nuts too are considered a valuable source.