NEUKO-MUSCULAR MECHANISM 



95 



stimuli are applied, and which tend to spread under the 

 influence of powerful stimulation, the spreading occurs along 

 definite lines for each type of stimulation. Thus, the ordinary 

 flexion-withdrawal of the foot on stimulation is at first confined 

 to the ham-string muscles, but, as the stimulus is increased in 

 strength, the movement spreads to involve the flexors of the 

 hip and knee, extension of the opposite hind leg, then exten- 

 sion of the fore limb of the same side and flexion at the elbow 

 of the opposite fore limb with some extension of the wrist, 

 turning the head towards the same side, often opening of the 

 mouth and lateral deviation of the tail. Thus a reflex figure 



FIG. 43. Reflex figures struck in decerebrated cat on stimulating a fore and 

 a hind paw. (SHERRINGTON. ) 



tends to be struck, and in the striking of this figure the 

 stimuli from the muscles and joints set up by each stage of the 

 movements probably play a very important part (fig. 43). 

 These definite channels of spread of reflex action appear to 

 have been developed by the progress of evolution. 



The Receptors. It is much more easy to elicit reflex action 

 by acting upon the neuron- termination than by acting upon the 

 nerve in its course. This may be demonstrated by observ- 

 ing the relative strengths of the pinch which it is necessary 

 to apply to the skin of the foot of the frog and to the 

 exposed sciatic nerve in order to produce a reflex contraction 

 of the muscles. The receptors have the property of lowering 



