462 



MANUAL OF PHYSIOLOGY. 



Among the vertebrata the duration of the contraction of the 

 skeletal muscles varies considerably according to the habits of the 

 animal. The limb muscles of the tortoise and toad take a very 



FIG. 187. 



Six curves drawn by the same muscle when stretched by different weights. 

 Showing that as the weight is increased the latency becomes longer and the 

 contraction less in height and duration. 



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. 



FIG. 188. 



Curves drawn by the same muscle at different temperatures. Showing 

 that with elevation of temperature the latency and the contraction become 

 shorter. (The muscle had been previously cooled.) 



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

 capable of considerable variation. It seems to be lengthened by 



