392 PROCESSES INFERRED FROM DIRECT OBSERVATION 



may be observed in a variety of ways. In the first place we may 

 excise the two corresponding leg-muscles of a frog, analyze one to serve 

 as a standard for resting muscle, and stimulate the other with a tetaniz- 

 ing current until exhaustion supervenes, and the muscle will contract 

 no longer, and then repeat the analysis upon this exhausted muscle. 

 The content of glycogen in the stimulated muscle is invariably found 

 to be lower than in the resting muscle, as much as fifty per cent, of the 

 glycogen being generally found to have disappeared. 



Another way of approaching the problem is to cut the motor-nerves 

 supplying one set of leg-muscles and, after the lapse of a definite period, 

 to compare the glycogen-content of these muscles deprived of nervous 

 connections with the glycogen-content of the corresponding normal 

 muscles on the other side of the body. The muscles of our skeleton, 

 while their nervous connections remain intact, are in receipt of con- 

 stant slight nervous stimuli, insufficient to elicit actual contractions, 

 but maintaining a condition of Tonus or constant tension which is a 

 favorable precedent to rapid and forcible movements. This tonic 

 contraction of the muscles of the skeleton consumes energy, not in the 

 performance of external work, it is true, but in the performance of 

 Internal Work; the overcoming of resistances analogous to friction or to 

 the resistance to extension which is displayed by a liquid surface. 

 This tonus and its resultant expenditure of energy are prevented by 

 cutting off the stimuli which maintain it, so that a muscle with its 

 motor-nerves severed, relaxes, and consumes less energy than a normal 

 muscle with its nervous connections intact. Corresponding with this 

 we find that the glycogen reserves in the paralyzed muscles tend to 

 accumulate and to exceed the glycogen-content of the innervated 

 muscles on the opposite, unoperated side of the body. This is clearly 

 shown by the following determinations by Marcuse upon rabbits, the 

 sciatic and crural nerves having been severed upon one side: 



. Percentage of glycogen. 



Experiment Paralysed Innervated 



Number muscles. muscle. 



1 0.748 0.539 



2 0.749 0.461 



3 0.589 0.395 



4 0.542 0.341 



Average 0.657 0.434 



The glycogen-reserve, through lack of expenditure, was therefore 

 increased fifty per cent, in the paralyzed and demobilized muscles. 



Again, we may compare the glycogen-content of all the tissues in 

 two similar animals, in the one after a period of rest, and in the other 

 after a period of intense muscular exertion, and we obtain again the 

 same result, namely a disappearance of glycogen with the performance 

 of muscular work. Thus Kiilz forced a large and well-fed dog, weighing 

 45.5 kilos, to draw a heavy cart for nine hours and forty minutes. The 

 animal was then killed, and the total glycogen-content of all its tissues 



