554 GENERAL PHYSIOLOGY 



muscle-energy lies in the decomposition of proteid, the latter must 

 be increased by extensive muscular activity. Since, now, it was 

 believed that an absolute measure of the extent of proteid-decom- 

 position in the body is to be found in the excretion of nitrogen in 

 the urine, the question would appear to be decided by a comparison of 

 the nitrogenous contents of the urine during rest and during ex- 

 treme muscular activity. If the nitrogen were increased during 

 work, the increase could be derived only from increased proteid- 

 transformation ; if it remained the same, the source of muscle- 

 energy was not to be sought in proteid but in non-nitrogenous 

 food-stuffs. The problem was, therefore, presented in a very clear- 

 cut form, and the decision could not be left to itself Fick in 

 company with Wislicenus ('65) showed upon himself, and Voit ('70, 

 '81) upon the dog, that the excretion of nitrogen in the urine is not 

 markedly increased by intense muscular activity. 



The question thus appeared to be answered very precisely. It 

 was concluded that the decomposition of proteid could not be the 

 sole source of muscle-energy. It was argued that of the non-nitro- 

 genous food-stuffs the carbohydrates especially, and eventually the 

 fats, must come into consideration ; and it was known that 

 with intense muscular activity the glycogen stored in the muscle 

 disappears, and accumulates again during rest. The argument 

 appeared wholly unobjectionable, and the view was generally ac- 

 cepted that muscle-energy is afforded chiefly by the decomposition 

 of carbohydrates. 



But the view that proteid does not take the chief part in the 

 extreme activity of the muscle-cell necessarily appeared parodoxical 

 to all who were at all familiar with the general vital char- 

 acteristics of living substance. Proteid is the substance with the 

 formation and decomposition of which life is inseparably associated, 

 and hence it seemed very remarkable that in augmented vital 

 activity, such as is represented by intense muscular movement, 

 the transformation of proteid was the same as during rest. Pfliiger 

 could not sympathise with this view. In a series of striking re- 

 searches, supported by experiments free from objection, he- recently 

 attacked it, and sought to establish proteid-decomposition as the 

 chief source of the energy of muscle. It was already known to 

 Voit that dogs can maintain themselves upon a meat diet alone. 

 Pfliiger ('91), therefore, fed a dog for many months exclusively with 

 meat, as pure and free from fat as possible, and made him perform 

 several times every day for weeks very difficult labour. The animal 

 showed continually " very extraordinary strength and elasticity in 

 all his movements." Since the slight traces of carbohydrates and 

 fat contained in the meat need not be considered in nutrition, it 

 was proved that all the energy produced during the hard labour of 

 the dog was derived from the transformation of proteid. But 

 in order to discover whether the proteid served simply as a 



