270 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 5 



degenerative changes in the epithelial cells which line the outer sur- 

 faces of the body, and among the characteristic symptoms which fol- 

 low upon such a lack is a pathological condition of the eyes known 

 as xerophthalmia. As an independent phenomenon, night blindness 

 may occur. Very noteworthy is the evidence which shows that an 

 adequate supply of this vitamin protects against certain types of in- 

 fection. One of the most interesting advances in our knowledge of 

 vitamins is the recent proof that vitamin A is closely related chemi- 

 cally to the carotenes, a group of yellow pigments widely distributed 

 in plant tissues, and the further proof that carotenes, when they are 

 consumed in green vegetables, are converted in the liver into the vita- 

 min itself. These discoveries have thus shown that vegetable foods 

 are an effective source of the vitamin, and they have also greatly 

 helped in leading to our present knowledge of its actual chemical na- 

 ture. It has been obtained pure in the form of an oil, and chemical 

 studies have revealed its essential molecular structure. 



Vitamin B^. — This is the vitamin of which a deficiency in the food 

 supply leads as a final issue to the disease beriberi. It exerts a general 

 influence in the body, and would seem to be essential to the normal 

 progress of carbohydrate metabolism, but a specialized aspect of its 

 functions is the maintenance of a normal equilibrium in the nervous 

 tissues. It is widely distributed in natural foods, but in concentra- 

 tions which vary greatly. We have seen that the circumstance of its 

 presence in the cortical parts of grains and absence from the en- 

 dosperm led, through the work of Eijkman and his followers, to one of 

 the earliest suggestions for the existence of vitamins. It is relatively 

 abundant in yeast, and this has been the material chiefly used as a 

 source of it for experimental work. Much effort in Great Britain, 

 in particular by R. Peters, has been spent in the effort to obtain it in 

 a pure state, an end which seems now to have been reached. Its actual 

 molecular structure is not yet known, but its empirical formula is 

 probably Ci2lIi6N40S. Alone among the known vitamins it contains 

 sulphur in its molecule. 



Vitamin Bn. — When yeast extracts were first employed as addenda 

 to deficient diets, their most notable effect, apart from the promo- 

 tion of growth, seemed to be the prevention of nervous lesions. 

 They were supposed to supply an " antineuritic " vitamin alone. 

 This is now Bi. Further studies of such extracts showed, however, 

 that they certainly contain at least one other vitamin more stable 

 toward heat than Bi, and clearly showing quite different properties. 

 In its absence serious skin lesions develop, resembling in animals 

 those seen in the human disease pellagra. There is now indeed little 

 doubt that a prominent factor in the causation of this disease is a 

 lack of this vitamin in the food. It has been labeled Bo. Quite 



