THE MUSCLES. 



559 



tractions is saturated with the so-called fatigue-products which have 

 poisonous properties. The chemical theory of fatigue is proved by 

 preparing a watery extract of muscles exhausted by a series of con- 

 tractions, and injecting this into the circulation of a frog. Here it 

 will cause the muscles to show fatigue in the same manner as when 

 spontaneously caused. This fatigue of the muscles in the frog, 

 caused by electric tetanus, can be removed and their irritability re- 

 stored by the injection of solutions of sodium carbonate into the vein. 

 This alkaline solution washes out the fatigue-products from the 



Fig. 203.* Mosso's Ergograph. (From Tiger stedt's "Human Physiol- 

 gy>" co py r ight, 1906, by D. Appleton and Company.) 



luscle. The circulation of blood normally washes away the toxic 

 >ducts of fatigue. Mosso has shown that the blood of a fatigued 

 j, when injected into the vein of another dog, caused all the symp- 

 )ms of fatigue. In the fatigued muscles of the frog it is not neces- 

 iry to have the blood wash away the products of fatigue, for it has 

 shown that the oxygen of the air in about half an hour can 

 store their irritability. If the muscle fatigued is placed in an 

 losphere of hydrogen, no restoration of the muscle ensues. Oxida- 

 tion is the restorative agent in fatigued muscles. 



THE SEAT OF THE FATIGUE. When a nerve of a warm-blooded 

 limal is curarized, artificial respiration being kept up, and' elec- 

 icity applied to the nerve, it causes no muscular response until the 

 (Hi-are is excreted, when the muscle again contracts, showing that it 



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