GENERAL MUSCLE PHYSIOLOGY 199 



sets in later in a muscle whose motor nerve has been cut 

 than in a muscle whose nerve has not been cut. 



Heat rigor, which takes place when a muscle is killed by 

 heating it above 40 C., is identical with rigor mortis. 



Physiological differences between smooth and striated 

 muscles. The smooth muscles differ physiologically from 

 the striated in the following points : 



1. The striated, except the cardiac muscles, are voluntary 

 muscles; the smooth, except the ciliary muscles of the eye 

 which function during accommodation, are involuntary. 



2. The smooth muscles contract more slowly and the 

 contraction wave is much longer than in the striated muscles 

 (see page 190). Of the striated muscles, the cardiac muscle 

 contracts more slowly than the skeletal muscles. But in 

 the cardiac muscle the striation is less perfect than in skeletal 

 muscles. The more nearly perfect the cross-striation the 

 greater the velocity of contraction. 



3. Smooth muscles are more readily stimulated by long 

 duration than by sudden changes in the intensity of the 

 electric current, while the striated muscles are more readily 

 stimulated by sudden changes in the intensity of the current. 



4. In the smooth muscle the stimulation passes from one n 

 fibre-cell to another, not so in the striated muscle (except ^ 

 cardiac). 



Protoplasmic and ciliary movement. 



i. Protoplasmic movement. White blood corpuscles, like 

 amoeba, change their shape by the thrusting out and draw- 

 ing in of pseudopods. By attaching a pseudopod to the 

 underlying surface and drawing the body along by the con- 

 traction of the protoplasm, they are also able to move from 

 place to place. During rest the pseudopods are withdrawn 

 and the cell is spherical. 



Within the limits of temperatures by which the cell is not 

 injured, the higher the temperature the greater the proto- 

 plasmic movements. At a temperature of a little above 

 40 C. the pseudopods are withdrawn ; in heat rigor the 

 cell is spherical. Lack of oxygen paralyzes. 



