FEEDING EXPERIMENTS WITH ISOLATED FOOD SUBSTANCES. 7 



and mice are reported to have been kept in health on milk alone 

 during periods of six months or more.* So far as we are aware no 

 experiments in which "artificial" food mixtures were introduced 

 have ever been carried on successfully for an equal duration. 



The most elaborate published nutrition experiments in respect 

 to the variety of important details taken into consideration are those 

 of Henriquesf on white rats. He determined the changes in weight 

 and the food-intake, as well as the complete daily nitrogen balance, 

 in a large number of animals fed on artificially mixed diets. The 

 isolated proteins used were casein, zein, and gliadin, with additions 

 of sugar, lard, cellulose, and inorganic salts. J Only with casein and 

 gliadin were the nitrogen balances favorable for the few days during 

 which each trial was continued. This was true despite the gradual 

 loss of body-weight noted in each case. It serves to emphasize what 

 is frequently overlooked, viz., that a favorable nitrogen balance over 

 a short period of time is in no sense an adequate index to a satisfac- 

 tory nutritive condition. We have found that the body- weight of the 

 rat is a more reliable guide to the real nutritive equilibrium of the 

 animals than is the nitrogen balance. jj 



Valuable as the experiments of Henriques and Hansen have 

 been for the purposes of orientation in a new field of research, the 

 failures can not be adduced as proof of the inadequacy of the pro- 

 teins selected, nor can the apparently successful results be accepted 

 as conclusive. For the latter point, the duration of the experiments 

 is far too short, as will be seen from the work of subsequent experi- 

 menters. The most serious criticism, perhaps, pertains to the food 

 intake, which must have been within the lower limits of a maintenance 

 ration for the animals which in many cases had not yet completed 

 their growth. In respect to one conclusion the words of Henriques 

 may be quoted : 



Wir linden also, dass es eine Wesensverschiedenheit zwischen der 

 Bedeutung des Zeins und der des Gliadins fur den Stiekstoffumsatz im 

 Korper gibt; das Zein vermag kein Stiekstoffgleiehgewicht herzustellen, 

 was dagegen das Gliadin vermag wenn es in reiehlieher Menge gegeben 

 wird. Der Grund dieser Verschiedenheit lasst sieh natiirlieh nicht mit 



*Falta and Noeggerath: Hofmeister's Beitrage zur chemischen Physiologie, 1905, 

 vii, p. 320 (rats). Knapp: Zeitschrift fur experimentelle Pathologie, 1908, v, p. 150, says: 

 "Bekanntlich konnen z.B. Mause mit Milch monatelang ernahrt werden und befinden 

 sich vvohl dabei." Socin: Zeitschrift fur physiologische Chemie, 1891, xv, p. 93, fed mice 

 99 days on egg yolk alone. 



fHenriques and Hansen: Zeitschrift fur physiologische Chemie, 1904-5, xuii, p. 

 417; 1908, liv, p. 169; Henriques: Ibid., 1909. lx, p. 105. 



tit should be noted that these included "Knochenmehl" (p. 419-420), which is not 

 entirely free from nitrogenous matter. Was bone-ash intended? 



||It may be worth while to point out here that we have found very considerable losses 

 of nitrogen, especially in hot weather, when urine is collected by the method adopted by 

 Henriques and by us, which will be described later. Such losses, amounting to 10 per 

 cent and over, would obviously lead to the assumption of a greater retention of nitrogen 

 than actually occurred and a consequent incorrect nitrogen balance. 



