56 FEEDING EXPERIMENTS WITH ISOLATED FOOD-SUBSTANCES. 



Monotony of diet has been urged as an obstacle to success where 

 the same food mixtures are daily furnished^ without change over long 

 periods of time. Very closely associated with this is the question of 

 the palatability of the diet. The two factors need, however, to be 

 distinguished. The palatability of the diet has, perhaps, been over- 

 emphasized in recent years in its bearing on the real nutritive value 

 of foods. It applies primarily to the individual with highly organized 

 nervous system and psychical functions. The quality found in foods 

 which are unpalatable because they disgust or nauseate is something 

 positive; the negative property of lack of palatability, i. c, absence 

 of stimulating taste, etc., is not necessarily a serious obstacle. In any 

 event the palatability of the diet is difficult to determine or regulate 

 and in attempting to control it experimentally in animals physi- 

 ologists have been guided very largely by anthropomorphistic con- 

 siderations. 



We have now gathered observations which lead us to dismiss the 

 idea that monotony per se leads to anorexia or other forms of nutri- 

 tive failure in our animals, despite the comment which this feature 

 has received from other investigators. There is no convincing reason 

 why a continued unvaried diet should necessarily be unphysiological ; 

 one need only recall the fact that the diet of all sucklings is the same 

 from day to day, and that many of the domestic animals are satis- 

 factorily maintained on rations which are scarcely altered in quali- 

 tative make-up except at long intervals. We have observed rats in 

 the same cage for considerably more than a year, during which the 

 daily diet was invariably furnished in the form of our food-pastes. 

 In some of these the composition of the paste was practically the same 

 during these very long periods (cf. Charts XXVII, XXVIII, XXIX, 

 XXX). It is true that we could point to many failures to maintain 

 rats on an unchanged diet continued over much shorter periods. One 

 must not, however, here confuse monotony with the real cause of 

 decline. In these latter cases some deficiency or defect in the monot- 

 onous feeding sooner or later brings on a physiological state where 

 anorexia occurs ; and the advantage which a change ofdiet initiates 

 ought primarily to be ascribed to the alteration in the food ingredi- 

 ents rather than the relief from the sameness of the intake. 



Among factors referring more directly to the nature of the food 

 itself, the physical texture and digestibility of the nutrients must be 

 taken into consideration. The structure of the food materials may, 

 under ordinary conditions of diet, influence its utilization in no small 

 degree; and the low "coefficients of digestibility" shown by many 

 foods of plant origin testify to this fact. In our experiments the 

 products fed were isolated and reduced to a state of very fine com- 

 minution. At most, therefore, some inherent indigestibility of the 

 individual foodstuffs employed might be concerned. Experiments 



