no THE PHYSIOLOGY OF PROTEIN METABOLISM 



only found an increase in the nitrogen output after work when 

 dyspnoea was induced, regarded the rise as secondary, and not as the 

 direct result of an increased catabolism of protein due to the actual 

 work. Frankel (137, 138) obtained the same result, and ascribed it 

 simply to the lack of oxygen. Voit (407) also observed this rise of 

 nitrogen excretion after dyspnoea, but thought that the muscular work, 

 arising from the struggle for breath, utilized all the available nitrogen- 

 free material, and then drew upon the tissue protein. Argutinsky 

 (53) observed a rise in the output of nitrogen, but not until some 

 three days after the work had been carried out. Liebig previously 

 had suggested that the rise in the output of nitrogen would not be 

 observed on the day of work, but later. This is apparently due to 

 the fact that a certain amount of damage is done to the cells by work, 

 and that cell restitution with the coincident excretion of effete material 

 is not a sudden act, but a comparatively slow one. Zuntz (427) 

 held that, so long as the nitrogen-free substances were present in the 

 food in abundance, the rise in the output of nitrogen would be but 

 slight. Munk (296) was also of opinion that the work was done 

 solely at the expense of the nitrogen-free food substances, and that 

 it was only when these were exhausted, or when dyspnoea was 

 induced, that work was followed by a rise in the output of nitrogen. 

 He explained all positive experiments in which work was followed 

 immediately, or later, by a rise in the nitrogen output on this hypo- 

 thesis. Kaup (216) found that, provided the supply of nitrogen- 

 free food was adequate, there was no increase in the breakdown of 

 protein during work. Hirschfeld (193, 194) found an increase in the 

 nitrogen output following work, only if the diet were deficient in 

 amount. Unfortunately Hirschfeld did not devote much care to the 

 nitrogen analysis of his foodstuffs and therefore his results cannot 

 be regarded as conclusive. 



Pfluger (328) fed a dog of about 30 kilos weight, doing severe work 

 for some seven and a half months, on flesh which contained only a 

 mere trace of fat and sugar. He concluded that protein alone was 

 sufficient to supply all the necessary energy, and that indeed 

 protein was the food par excellence fat and carbohydrate would only 

 be utilized, when all protein supplies failed. In this animal a slight 

 rise in the output of nitrogen was always observed after work, but it 

 was certainly not commensurate with the amount of work done. 

 Further, the rise, such as it was, did not take place on the day of 

 work, but on the second and third days following the exercise. In 

 his conclusion Pfliiger stated definitely that there was no work with- 



