THEORIES OF PROTEIN METABOLISM 93 



the breakdown of carbohydrates, were for some reason or another in a 

 state of suspension, inoperative or actually destroyed, whereas those 

 which 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 in- 

 ternal oscillations 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 con- 

 ditions of the organism itself. 



Speck. 



Speck (380), in 1903, also expressed his belief that two forms of 

 protein existed, but his idea of their subsequent fate was rather curious. 

 The part of the protein of the food, which was not utilized for the forma- 

 tion of new tissue (living protein), was broken down into a nitrogen-con- 

 taining part, which was rapidly converted into urea, and a nitrogen-free 

 rest, which was readily used as a source of energy. The tissue protein, 

 after the death of the cell, was also converted into a nitrogen-contain- 

 ing and a nitrogen-free part, but the subsequent fate of these two parts 

 was different. The nitrogen-free part under normal conditions was 

 converted into a fat or carbohydrate-like substance and utilized for 

 energy purposes. The nitrogen-containing part was not immediately 

 converted into urea, but it formed a great variety of substances, which 

 played an important part in metabolism and which were eventually 

 excreted as urea. He believed that oxygen deficiency played an all- 

 important role in the breakdown of the tissue protein. 



