FEEDING EXPERIMENTS WITH ISOLATED FOOD- 

 SUBSTANCES. 



PART II. 



INTRODUCTION. 



In Publication 156 of the Carnegie Institution of Washington* 

 we have discussed some of the problems of nutrition which have 

 been raised by the newer investigations in the field of protein chem- 

 istry. The literature bearing on the feeding of isolated proteins was 

 there reviewed in some detail, together with critical considerations of 

 previously available experimental data. We described a plan for 

 the study of metabolism and illustrated a method of investigation 

 in which white rats were the experimental animals. For the details 

 involved, our earlier paper must be consulted. A few protocols were 

 there presented to show that the outlined mode of investigation 

 offered a promising means for attacking certain questions in the 

 field of nutrition. 



INFLUENCE OF VARIOUS CONDITIONS ON NUTRITION OF WHITE RATS. 



Numerous contingencies may arise to modify or vitiate the re- 

 sults of experiments in which animals are kept in cages and fed upon 

 artificially prepared mixtures of isolated food-stuffs, quite independ- 

 ent of the factors inherent in the food-stuffs themselves or the com- 

 binations in which they are exhibited. Among these possibilities, the 

 caging itself, involving continued restraint and limited opportunity 

 for exercise, suggests an unfavorable environment. This factor can 

 at length be disposed of. 



Donaldson has concluded, from the best data obtainable, that 

 "the three-year-old white rat is very old, and is justly comparable 

 to a man of 90 years. "f Rats have been kept in our cages in appar- 

 ent good health and without difficulty during periods of more than 14 

 months a very considerable part of the span of life in these animals 

 (cf. Charts XXIII, XXIX, XXX). 



*Feeding experiments with isolated food-substances, by Thomas B. Osborne and 

 Lafayette B. Mendel, with the eo-operation of Edna L. Ferry. 191 1. Pp. 53. 



fH. H. Donaldson: A comparison of the white rat with man in respect to the growth 

 of the entire body. Boas Memorial Volume, New York, 1906, p. 6. 



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