VARIATIONS IN THE SINGLE CONTRACTION. 



.465 



long time to finish their contraction ; other muscles of the same 

 animals act more quickly, but do not attain the rapidity of con- 

 traction of the skeletal muscles of warm-blooded animals. 

 The duration of a single contraction of the same muscle is also 



FIG. 188. 



Curves drawn by the same muscle at different temperatures. Showing that with ele- 

 vation of temperature the latency aud the contraction become shorter. (The muscle 

 had been previously cooled.) 



capable of considerable variation. It seems to be lengthened by 

 anything that leads to an accumulation of the chemical products 

 which arise from muscle activity. Hence fatigue or over-stimu- 

 lation cause a slow contraction (Fig. 186). 



FIG. 189. 





Curves drawn by the same muscle while being cooled. Showing that the latency and 

 the contraction become longer as the temperature is reduced. 



Moderate increase of temperature greatly shortens the time 

 occupied by the single contraction of any given muscle. Exces- 

 sive heat causes a state of continued contraction. 



