ii2 THE PHYSIOLOGY OF PROTEIN METABOLISM 



increase in the output of nitrogen. He observed that the rise in the 

 nitrogen output was preceded by a rise in the output of sulphur. 

 Engelmann (119) also found an early rise in the output of sulphur as 

 the result of exercise. 



Frank and Gebhard (135) attacked the problem in another way. 

 They argued that if the muscular metabolism were reduced below nor- 

 mal, by the injection of curare, there would be some^effect on the en- 

 dogenous nitrogen exchange. Accordingly they curarized a dog and 

 found that the nitrogen output was reduced about 25 per cent. They 

 held that their experiments demonstrated that a certain preparation, 

 or storing, of material took place, so that the organism was always 

 ready for activity, but their argument is extremely difficult to fol- 

 low. Frank and Voit (136) had previously shown that the carbon 

 exchange was hardly altered by the giving of curare. 



Differences between Voluntary and Involuntary Muscle 



Contraction. 



There would seem to be, however, the possibility of two different 

 forms of work which affect the metabolism differently that associ- 

 ated with the voluntary contraction and that with the involuntary. 

 Leathes and Cathcart (248) demonstrated that the whole course of 

 purine excretion can be modified by alterations in the intensity of the 

 involuntary work. In these experiments shivering was utilized as the 

 form of involuntary work. It was found that if a subject doing the 

 minimum amount of voluntary work were exposed to cold, so that 

 severe shivering was induced, a very marked rise in the output of uric 

 acid followed, whereas when involuntary work was reduced to a mini- 

 mum and voluntary work carried out even to excess, there was just as 

 marked a fall in the output of uric acid. In both sets of experiments 

 the food was identical, sufficient in amount, and purine-free. 



Another interesting point of difference in muscular metabolism 

 which has been pointed out by Graham Brown and Cathcart (75) and by 

 Pekelharing and Van Hoogenhuyze (325), is that white muscle always 

 contains more creatine than red muscle. The latter observers calcu- 

 late that there is at least one-fourth more creatine present in white 

 muscle than in red. 



