PROTEIN METABOLISM 91 



dealt with the catabolism of fat were active. The 

 direct effect of the approximation of the foodstuffs 

 to the 'affinities' resulted in an atomic rearrangement 

 and the entry of oxygen. The potential energy of the 

 foodstuff now became available and caused a complete 

 alteration in the 'affinities'; an absorption of energy 

 into the living substance took place at the moment of 

 the catabolism of the foodstuff. The internal oscilla- 

 tions and changes in the cells, however, gradually used 

 up all the energy, which was converted into heat and 

 lost, and there was a return to the original condition, 

 the 'affinities' being again ready to begin work. The 

 rate of the change depended on the nature of the 

 living substance, the temperature, nervous influences, 

 and the conditions of the organism itself." (Cathcart.) 



FOLIN 



It was Folin's conception that "the laws governing 

 the composition of the urine represent only the effects 

 of other more important laws governing the catabo- 

 lism of protein in the animal organism" which led 

 him to determine these laws under widely differing 

 conditions of diet. His interpretation of protein 

 metabolism on the basis of observed variations in the 

 percentage composition of the urine has stood as the 

 almost universally accepted theory of protein metabo- 

 lism of the present period. 



Previous to his investigation only lengthy and none 

 too accurate methods were in use for the estimation 



