NUTRITION. 433 



of substances represented by the vitamins, it seems reasonable to 

 assume that pure fats are dispensable constituents of the mammalian 

 diet. We have already pointed out that the results of the foregoing 

 investigations lead one to question seriously the contentions made, 

 particularly during the recent war, that fats as such play some unique 

 role in maintaining well-being, and further (as Maignon supposes) 

 that they play an important role in the utilization of protein — a role 

 which carbohydrates are powerless to fill. On the other hand, our 

 experiments should not be construed to minimize the great value of 

 fats as a source of energy in the usual human dietary, as well as their 

 peculiar advantage in culinary procedures. 



Carbohydrates have heretofore been regarded as indispensable 

 components of the food intake. It has been almost universally 

 taught that carbohydrate is essential for the proper metabolism of 

 fats, for ketone substances may be excreted in diabetes when sugar 

 fails to be burned up in the normal manner in the organism. On 

 the other hand, it has been assumed that glucose can be formed from 

 the protein molecule, or its ammo-acids, under certain conditions in 

 the metabolism, so that one could conceive carbohydrate to become 

 available for the special needs of fat metabolism and other purposes 

 without being specifically furnished as preformed carbohydrate in the 

 diet. 



By the use of rations consisting of protein (casein, edestin, or lean 

 beef which had been thoroughly extracted with boiling water), inorganic 

 salts, agar-agar, lard, butter fat, and 0.4 gram daily of dried brewery 

 yeast, to furnish vitamin B, we have succeeded in making animals 

 grow from early age to adult size on mixtures of nutrients in which 

 the amount of digestible carbohydrate was at most exceedingly small. 

 In some of these trials the rats have reached a weight of 360 to 440 

 grams in less than 160 days, thus showing a growth rarely excelled on 

 our standard diet. In order to reduce the carbohydrate impurities 

 in the diet still further, feeding trials have also been conducted with 

 mixtures in which the proteins were purified until they were carbo- 

 hydrate free, and vitamin B was supplied by a yeast concentrate free 

 from demonstrable quantities of reducing carbohydrate. The other 

 ingredients of the ration — fats and inorganic salts — were obviously 

 also carbohydrate-free. The foods used in this series of experiments 

 represent the highest degree of freedom from carbohydrate attainable 

 at present; yet even on such mixtures rats already have grown at a 

 normal rate to 270 grams. Inasmuch as it is generally assumed that 

 diets devoid of carbohydrate readily lead to ketonuria, the urine from 

 several of the animals on these carbohydrate-free diets was tested for 

 acetone and diacetic acid, with negative results. Furthermore, a 

 chemical analysis of the entire bodies of some of the animals has shown 

 them to contain practically as much glycogen as is found in the tissues 



