FEEDING EXPERIMENTS WITH ISOLATED FOOD SUBSTANCES. 



19 



DISCUSSION. 



It will be noted that Rats xn and xin, representing different 

 ages, if we judge from the initial weights, were maintained in nutri- 

 tive equilibrium without loss of body- weight during the period of 147 

 days a not inconsiderable fraction of the life span of these animals. 

 There is, however, a gradual decline in the amount of food which is 

 eaten toward the end of the experiment, the quantity in the case of 

 xii approaching limits which must have necessitated some demand 

 upon the fat supply earlier accumulated. The utilization of the 

 protein continued satisfactory, thus evincing unimpaired digestive 

 powers It is far from likely that the ration used, with its large 

 preponderance of energy in the form of fat, is an ideal one. The facts 

 recorded, however, exclude the probability that monotony of diet 

 is an insurmountable obstacle to nutritive success.* 



As to the possibility of prolonged feeding on a uniform unchanged 

 diet, two illustrations are appended of experiments on rats 14 and 

 18 fed with a mixture of ground hempseed, starch, lard, and salts. 

 These rats were first fed with a mixture of dog biscuit and lard for 

 several weeks and then on the hempseed mixture. The composition 

 of the food given during the different periods is shown in table III. 

 Table III. Composition of the Food in Percentages. 



The figures for nitrogen are averages of the different batches of 

 food which were made up from time to time. The hempseed meal was 

 freed from the greater part of the hulls by sifting, but the different 

 lots contained different proportions which escaped separation ; hence 

 the actual nitrogen content of the individual batches of food varied 

 somewhat. The figures given in the protocols and representing daily 

 averages are based on the actual quantity of nitrogen fed, not on 

 the averages given in table III. 



*Among the many often unapparent difficulties which beset such experiments, the 

 frequent occurrence of intestinal parasites and the susceptibility of the animals o 

 digestive disturbances are to be noted. 



fThe salt mixture 1, which contained organic and inorganic salts of the necessary 

 bases and acids, is described on page 32. 



