466 GENERAL PHYSIOLOGY 



That which appears especially interesting is the fact, discovered by 

 Valentin ('47), and Eduard Weber ('46), that excised muscles also 

 are capable of recovery. This, also, can best be seen by the aid of 

 the graphic record of the muscular movement. If an isolated 

 gastrocnemius of a frog be fatigued by being alternately tetanized 

 for perhaps five seconds and allowed to rest for five seconds, after 

 some time, the intensity of the stimulus remaining constant, 

 the curve begins to fall, until, finally, the stimulation no longer 

 produces any contraction, and the muscle remains at rest in a 

 slightly contracted condition, determined by the contraction- 

 remainder. If, then, the stimulation be interrupted and the 

 muscle be left to itself for a considerable time, protected from 



FIG. 241. Ganglion-cells of the sparrow. A, Morning ; B, evening. (After Hodge.) 



drying, contractions nearly equal to those before the fatigue can 

 be induced anew with the same strength of stimulus. The 

 muscle now becomes fatigued more rapidly than before. One 

 factor in the recove'ry, which has recently been established in 

 Richet's laboratory by J. Joteyko ('96), is of interest. This is 

 found in the fact that excised muscle recovers only when oxygen 

 is available ; with the exclusion of oxygen after complete fatigue 

 the muscle cannot be put again into activity. Hence oxygen is 

 absolutely necessary for the restoration of the irritability of muscle. 

 But the fact that after great fatigue excised muscle is able to 

 recover in a medium containing oxygen proves that the muscle- 

 substance, while it can perform contractions for a considerable 

 time independently of the circulating blood, must possess in itself, 



