272 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 5 



increased by exposure to rays of suitable wave length. A preparation 

 of the vitamin made by the irradiation of ergosterol in vitro is known 

 as " calciferol." Its potency is remarkable ; one ten-thousandth of 

 a milligram a day added to a rickets-producing diet will in a rat 

 entirely prevent the appearance of the disorder. In the case of a 

 child the effective daily dose is a very small fraction of a grain. The 

 rigorous proof that lack of a fat-soluble vitamin is responsible for 

 the induction of rickets was furnished by the classical experiments 

 of E. Mellanby begun 20 years ago. More recently the importance of 

 vitamin D in the processes of normal dentition has been shown by 

 May Mellanby. 



Vitamin E. — In 1922 it was first shown by H. M. Evans and 

 K. S. Bishop that a vitamin, distinct from others then known, is 

 essential for successful reproduction. It has been termed the anti- 

 sterility vitamin, but this term implies functions more specific than 

 those which are actual. Deprivation of vitamin A, for example, 

 will ultimately lead to failure in reproduction. Nevertheless, the 

 influence of vitamin E (now so-called) is exerted on specific lines. 

 In its absence there is degeneration of the testes in the male and a 

 failure of the placental functions in the female. The richest sources 

 of this vitamin so far discovered are certain green vegetables and 

 wheat embryos. It is, however, widely distributed in foodstuffg, 

 and as it is active in very small amounts, the possibility of any lack 

 of it can seldom arise. Its constitution is unknown. 



These very brief descriptions of the known vitamins leave out, of 

 course, a multiplicity of facts which have been discovered concern- 

 ing each of them, and omit reference to the work of very many inves- 

 tigators. They may serve, however, to indicate the lines on which 

 vitamin research has hitherto progressed. 



Characteristic of each vitamin is the very small amount in which 

 it exercises its physiological functions, and the circumstance that 

 all are present in very low concentrations in the materials from which 

 they have to be separated has greatly added to the difficulties of their 

 study. It will be admitted, however, that we have now a sound body 

 of knowledge concerning them, establishing their nutritional im- 

 portance and throwing no little light on their nature. Research in 

 the field is now receiving much help on its constitutional side from 

 modern physical methods, and on its biological side from increasing 

 interest on the part of a large number of clinicians. Vitamin 

 therapy is now joining hands with endocrine therapy, and the League 

 of Nations Permanent Commission on Biological Standards has 

 recognized its growing importance by accepting standards for meas- 

 ures of vitamin activity and defining units in terms of such 

 standards. 



