436 CARNEGIE INSTITUTION OF WASHINGTON. 



to each other offered equal opportunity for the dissemination of con- 

 tagion among all of them. We have, however, failed to observe 

 symptoms of ophthalmia except in rats on diets deficient in the fat- 

 soluble vitamin. This is the more striking inasmuch as a large number 

 of the animals were suffering from other deficiencies in their foods which 

 presumably might make them equally susceptible to contagion. The 

 different stages of ophthalmia associated with a deficiency in vitamin 

 A has been the subject of a highly interesting report by Dr. Wason 

 (Jour. Amer. Med. Assn., 1921, vol. 76, 908), who has studied a large 

 number of cases developing in our animals. 



In our experience cessation of growth and ophthalmia have rarely 

 appeared until the animals have been fed for a number of weeks on 

 diets lacking vitamin A. Other investigators, however, have described 

 far more prompt cessation of growth and nutritive decline upon such 

 diets. Our results have accordingly been criticized on the ground 

 that our diets could not have been sufficiently purified and must have 

 contained a small, although not negligible, trace of this essential food 

 factor. Inasmuch as we have demonstrated that fat jper se is not 

 essential for life, we have undertaken an entirely new series of experi- 

 ments with diets from which fat and presumably vitamin A were 

 entirely eliminated. The protein and carbohydrate were repeatedly 

 extracted with hot alcohol and ether until the extracts left no signifi- 

 cant residues when evaporated. Upon food mixtures containing such 

 protein and carbohydrate, together with inorganic salts and small 

 quantities of brewery yeast (already demonstrated to be devoid of 

 vitamin A), the characteristic signs of deficiency have usually appeared 

 only a few days earlier than in our previous experiments. We are 

 forced to conclude, therefore, that other factors than the relative purity 

 of the rations may modify the rate of onset of the deficiency symptoms 

 in different colonies of animals. It is possible that the initial growth 

 of our animals may be, in part at least, due to the fact that a sufficient 

 consumption of the water-soluble vitamin was in all cases assured by 

 feeding tablets of brewery yeast apart from the food, whereby the in- 

 take of vitamin B was wholly independent of the food intake. On 

 several occasions we have observed in animals under conditions where 

 both vitamins A and B have been supplied by a single source, such as 

 alfalfa, and a slowing of growth properly attributable to a shortage of 

 either vitamin ensued, that a renewal of growth promptly followed on 

 feeding a small amount of yeast. This illustrates the importance of 

 assuring an adequate intake of vitamin B whenever a possible deficiency 

 of other vitamins is in question. 



To determine the effect of the maternal diet during pregnancy upon 

 the subsequent growth of the offspring, pregnant females were placed 

 at various times prior to parturition upon diets practically devoid of 

 vitamin A. When the young were born they were thus compelled to 



