422 JOHN LINCK ULRICH 



contraction phase for extensor thrusts wears out especially rap- 

 idly when the reflex excitability of the decerebrate preparation 

 is low, and seems to wear out more rapidly than the inhibition 

 phase. This wearing out of the contraction phase for the exten- 

 sor thrust can scarcely result from changes taking place in the 

 neural centers alone. The efficiency of the organism being nota- 

 bly dependent upon reflex excitability, it appears that the 

 chemical correlates secreted at this time are subnormal in amount, 

 and the effects of fatigue are not lessened. Gruber (18) has 

 shown that with epinephrin profusion of the body musculature, 

 an invigoration of the musculature is apparent. It may be sup- 

 posed with a subnormal production of epinephrin, an invigoration 

 of the body musculature does not take place. Possibly a de- 

 crease in the efficiency of the reflex musculature can more defi- 

 nitely be said to be traceable to a quantitative subnormal pro- 

 duction from other endochrine glands than that of the adrenal 

 glands. That other glands function likewise in the invigoration 

 of striated muscles is in accord with the researches of Rogers, 

 Cooms, and Rahe (19). Intravenous injection of non-coagulable 

 portions of alkaline extracts of fresh thyroids, parathyroids, and 

 adrenal glands increase the vigor of contractions of fatigued 

 voluntary muscles. It appears that a subnormal production 

 of a number of glands accounts for exhaustion in rats. 



From these experiments on the endochrine secretions during 

 fatigue, apparently the direct effect of the substances secreted 

 is upon the muscle fibers and not upon neural centers. Accord- 

 ing to Pratt (20), during muscular fatigue there takes place an 

 elimination of contractile elements. It is possible that endo- 

 chrine secretions invigorate the muscle fibers that tend to be 

 eliminated. With the appearance of fatigue and a subnormal 

 production of endochrine secretions, an elimination of contrac- 

 tile elements would prevent the production of effective posture 

 to produce the neck reflex movement. 



The two reflex mechanisms, the reflex extensor thrusts of the 

 rats limbs, and that for the production of reflex excitability, do 

 not stand alone, for excitations in the sensory mechanism must 

 evoke responses. The senses are directly concerned in initiating 



