REGULATORY SUBSTANCES 515 



Vitamin D. — Vitamin D has received much attention of late 

 because of the serious effect of its absence on children. Rickets 

 results from vitamin D deficiency. This vitamin is the principle 

 directly concerned with maintaining the calcium and phosphorus 

 balance of the blood at the normal level and hence with the 

 calcification of the bones of the body. McCollum first demon- 

 strated the effect of cod-liver oil on a low-calcium and high- 

 phosphorus rickets. 



Vitamin D is most abundantly found in cod-liver oil. As an 

 antirachitic agent, this oil has a perfect counterpart in the ultra- 

 violet component of sunlight. Vitamin D is found in some few 

 other animal products (egg yolk, butter, milk) but not in plants. 

 The activation of ergosterol results in the production of vitamin 

 D (see page 465). 



Vitamin E. — Animals confined to a certain ration often become 

 sterile in the later stages of reproduction. The embryo dies, 

 usually soon after the twelfth day of fetal life. A definite food 

 requirement is needed by the developing young, and this is now 

 known to be vitamin E. This antisterility vitamin is present in 

 small quantities in animal tissue but much more abundant in 

 plants, its potent source being wheat-germ oil. 



Vitamin G. — Vitamin B has been found to consist of two 

 principles, both active in nutrition. The first, or antiberiberi 

 factor, retains the designation B. The second has been termed 

 both B2 and G. Its presence prevents pellagra, a disease of 

 southern Europe characterized by erythema and nervous and 

 digestive orders. Vitamin G, or B2, is widely distributed in 

 plants and is usually associated with B. The richest carrier of 

 both is yeast, although cottonseed meal is the cheapest source of 

 the pellagra-preventive vitamin G as well as of vitamin B. 



Chemical Constitution of the Vitamins. — Several of the vita- 

 mins have been obtained in the crystalline state, and one has 

 been synthesized. We are thus very near to an understanding 

 of their constitution. The chemical nature of vitamin A is 

 known with a high degree of probability. It is not a sterol, as 

 are vitamins D and E, but rather a phytol-like compound. The 

 formula on page 516, by Karrer, is generally accepted. (There 

 is a suggestion of isoprene structure in the side chain on the 

 beta-ionone ring.) The constitution of a long carbon chain 

 attached to a ring relates vitamin A to certain vegetable pig- 



