434 CARNEGIE INSTITUTION OF WASHINGTON. 



of rats fed to maturity on the standard laboratory diets in which an 

 abundance of carbohydrate is always present. Evidently, therefore, 

 the rat at least can manufacture the physiological quota of tissue 

 carbohydrate from non-carbohydrate material, presumably the amino- 

 acids. 



With the dispensability of either carbohydrate or fats for the pur- 

 poses of growth thus demonstrated, we fed a diet of which more than 

 90 per cent consisted of protein, along with 5 per cent of inorganic 

 salts and vitamins in the form of small daily doses of dried alfalfa 

 and brewery yeast. In these trials, still in progress, in which the vita- 

 min-bearing substances, representing 4 to 8 per cent of the food 

 eaten, were the only noteworthy sources of either fat or carbohydrate, 

 some animals have grown at more than the normal rate to about 

 225 grams; subsequent growth, however, has been decidedly slower, 

 so that the final outcome can not yet be forecast. 



In all of the experiments on the unusual diets reported in this com- 

 munication the protein content of the food mixtures was unusually 

 high. An abundance of protein in the dietary during growth may be 

 actually advantageous, rather than detrimental as has been suggested 

 by certain writers. Although our experiments have not been continued 

 long enough to show whether animals will attain full adult size and 

 normal function on these high protein diets, they do raise a number of 

 important problems of physiological interest and also suggest new 

 possibilities from novel standpoints in connection with intermediary 

 metabolism. 



That animals tolerate a high concentration of carbohydrate in the 

 diet is a matter of e very-day observation. The foregoing experiments 

 have shown a similar toleration of a high concentration of protein. 

 Tradition, on the other hand, teaches that large quantities of fat are 

 not so well tolerated. It must be borne in mind, however, that be- 

 cause food intake is limited by the energy requirement, animals eat a 

 comparatively small quantity of foods rich in fats; consequently, when 

 such a diet is consumed too little of the proteins, salts, and vitamins 

 may be eaten. We have fed mixtures containing as high as 75 per 

 cent of fat in the diet without carbohydrate, the remainder of the mix- 

 ture consisting of protein and inorganic salts in such proportion as to 

 enable the animal to secure a sufficient amount of these food factors. 

 Enough vitamin B was supplied by daily feeding weighed quantities 

 of yeast apart from the food mixture. Fats yielded about nine-tenths 

 of the calories eaten by the rats thus fed. Although only a beginning 

 has been made in this field of investigation, which presents various 

 possibilities of importance for physiology and pathology alike, these 

 experiments already demonstrate that large quantities of fat offer no 

 insurmountable difficulties, even in the absence of preformed carbo- 

 hydrate, which is ordinarily considered to be indispensable for the 

 metabolism of fats. 



