560 PHYSIOLOGY. 



is not the nerve or the muscle, but the motor end-plates, which are 

 exhausted. Mosso has shown that if, with the ergograph, you lift a 

 weight until the flexor muscle is exhausted, and then induction cur- 

 rents are applied to the nerves going to the muscle, the muscle will 

 again lift the weight. This experiment shows that the fatigue- 

 products generated in the muscle are carried by the circulation to 

 the central nervous system and poison it. Hence the central nervous 

 system is shown to be the chief seat of fatigue, and the motor nerve- 

 endings the next. 



A B 



Fig. 204. Ergographic Curves. (After Mosso.) (From Tiger- 

 stedt's "Human Physiology," copyright, 1906, by D. Appleton and Com- 

 pany. ) 



Read from right to left. 



Ergographic Curves. The most salient feature seen in them is 

 the rhythmical rise and fall, which is due to the central nervous sys- 

 tem. During the first 180 contractions the height of the ergographic 

 curve decreases, and then becomes nearly constant in the height, which 

 is above 85 per cent, of the original contraction. 



The curve indicates that during a series of contractions two pro- 

 cesses are at work, the one using of material and the other an accu- 

 mulation of fatigue-products in the first part of the curve. In the 

 subsequent part of the curve, the fatigue-products are removed by 

 the circulation, and the circulation supplies the materials to be 

 used up. 



