FEEDING EXPERIMENTS WITH ISOLATED FOOD SUBSTANCES. I I 



More interesting even are his studies on the growth of young 

 rats. They made considerable gains in weight in experiments with 

 the proteins mentioned without casein in one series and with it 

 in the other and extending over from 56 to 127 days. But the 

 curves of growth do not approach those obtained for normal diet 

 by Donaldson, to which we shall have occasion to refer again. 

 McCollum concludes that "the palatability of the ration is the most 

 important factor in animal nutrition" and "the failure of previous 

 efforts to maintain animals on a mixture of relatively pure proximate 

 constituents of our food-stuffs was due to the lack of palatability of 

 such mixtures." 



Finally reference must be made to the very successful attempts 

 of Rohmann.* The details have not yet been published. Mice could 

 be kept indefinitely on a mixture of casein, vitellin, egg albumin, and 

 non-nitrogenous nutrients. They became mature and produced 

 young which thrived. With only a single protein in the ration, a 

 decline soon set in. If casein and egg albumin were used to replace 

 each other the grown mice retained their weight, but the devel- 

 opment of the younger ones was checked and they succumbed. 

 Rohmann concluded from these facts that the different proteins 

 possess a different significance for the nutrition and the development 

 of young organisms. 



Although none of our predecessors has returned a decisive 

 answer to the fundamental question whether any single protein or 

 combination of proteins is incapable of supplying all the essential 

 chemical complexes which the body is unable to furnish to itself by 

 direct synthesis, the pursuit of a solution by no means appears futile. 

 None of the difficulties actual or assumed which have arisen 

 appears experimentally insurmountable at present. The digesti- 

 bility and utilization of the artificial rations has never been demon- 

 strated to be abnormal or even unfavorable. The texture and 

 inclusion of "roughage," such as is ordinarily a part of every mixed 

 dietary in the guise of cellulose, can be experimentally adjusted, if 

 indeed it is of any serious moment in controlling the mechanical 

 functions of the alimentary tract. 



Monotony of diet appears to have been overemphasized, if one 

 may judge by the success with which milk or egg yolk have constituted 

 the only food material for rats and mice. The failure common to all 

 of the recorded experiments has been attributed to the difficulty of 

 inducing animals to eat sufficient food. Strictly speaking, it has not 

 been determined as yet whether the notable anorexia is the result 

 of some unpalatable feature of the artificial food mixtures and thus 

 the cause of the gradual inanition, or whether it is really a physio- 

 logical sequence of an imperfect dietary. 



*R6hmann: Allgemeine Med. Central-Zeitung, 1903, No. 1; 1908, No. 9. Cf. 

 Maly's Jahresbericht, 1903, xxxin, p. 823; 1908, xxxvm, p. 659, for the same abstracts. 



