NUTRITION. 435 



It has been known for some time that considerable quantities of 

 fatty acids can be utilized as food, and that during absorption they are 

 converted into neutral fats, the glycerol thus required possibly being 

 synthesized de novo in the organism, in which case the presence of 

 carbohydrate may be essential. In view of the satisfactory growth 

 made by animals on diets free from carbohydrates or fats, we are now 

 undertaking investigations of the utilization of fatty acids in various 

 proportions, with or without available glycerol or carbohydrate, in 

 the dietaries. It is too early to foretell the results of these experiments. 

 Owing to the need of fats during the Great War for the production of 

 glycerol, and the corresponding accumulation of fatty acids, the possi- 

 bility of the use of the latter for food purposes became a problem of 

 national importance. 



For more than a year we have been conducting an extensive series 

 of feeding trials in which the only variable, aside from the variations 

 in the voluntary daily food intake, has been the amount of vitamin B 

 fed daily, as dried brewerj'- j'-east tablets, apart from the rest of the 

 ration each day. 200 milligrams of this yeast per day sufficed at all 

 ages for growth or maintenance, in so far as one can judge by body- 

 weight and general appearance. With 100 milligrams per day young 

 rats grew at a normal rate until about three-fourths the usual adult 

 size was attained, but thereafter they ceased to gain in weight. When 

 the daily yeast intake was reduced to 50 and to 25 milligrams respec- 

 tively per day, growth was correspondingly slowed, so that w^ith the 

 smallest portions noted little more than maintenance has been secured 

 after a few weeks of initial growth, although very young animals do 

 grow for some time at a fairly good rate when receiving the minimal 

 quantity of yeast just recorded. 



Tests for the presence of vitamin B have been made with a variety 

 of products in addition to those which we have previously investigated. 

 Thus it has been found that dried strawberries, lettuce, and asparagus 

 contain less vitamin B than does dried brewery yeast, inasmuch as at 

 least 0.4 gram of these is required to produce the same effect as is 

 readily obtained with one-half or less of this amount of dried yeast. 



In view of the questions which have frequently been addressed to us 

 regarding the desirability of long-distance shipments of dried milk, 

 especially from the standpoint of its vitamin content, it is worthy of 

 note that we have grown rats from 70 grams to full adult size on a diet 

 consisting for more than a year solely of dried whole-milk powder, 

 corn-starch, and lard. 



It has been claimed that the ophthalmia which so frequently develops 

 in animals fed on diets free from vitamin A is due primarily to infec- 

 tion rather than to a dietary deficiency. In this connection we have 

 reviewed the incidence of this eye disease in 1,000 rats taken seriatim 

 from our colony and representing essentially an entire group studied 

 during one year under conditions in which the proximity of the animals 



