MOTOR NERVES AND MUSCULAR CONTRACTION. 251 



Considered as motor constrictors these nerves would respond 

 to stimulation in precisely this manner. "Exposure to a low 

 temperature again seems to depress the constrictors more than 

 the dilators; hence, when the leg is placed in ice-cold water 

 stimulation of the sciatic even when the nerve has been but 

 recently divided, throws the dilator only into action, and pro- 

 duces flushing of the skin with blood." This demonstrates at 

 least an intimate association between motor and constrictor 

 functions. Again, since placing of the limb in ice-cold water 

 abolishes response, of the sciatic to stimulation, this nerve must 

 readily succumb functionally to untoward influences evidently 

 sooner than the vasodilator. This is confirmed by the state- 

 ment: "The latter" (the vasodilators), "in contrast to ordinary 

 motor nerves, retain their irritability after section of the nerve 

 for very many days." Again does the link between the motor 

 and the constrictor element appear, and as they jointly suc- 

 cumb while the dilators retain their irritability, and the loss 

 of function under pathogenic influences begins much sooner 

 than in the latter, we are brought to recognize, first, that motor 

 and constrictor nerve-elements are either pathologically af- 

 fected in precisely the same manner, or that both functions 

 are attributes of the motor nerve; second, that we have in the 

 histological changes incident upon section of the latter, or the 

 nerves of the brachial plexus, the cause of vascular dilation 

 that ensues upon stimulation, when this experimental proced- 

 ure is not carried out at once. 



And, indeed, the strength of this proposition appears if 

 we examine the histological structure of any nerve-bundle, and 

 particularly such organs as the sciatic. The many elements 

 that enter into their organization suggest immediate morbid 

 alterations on section, especially if our view that the blood- 

 plasma is the vehicle or excipient of the oxidizing substance 

 which maintains all functional processes is warranted. Under 

 these conditions, it is plain that cutting of the nerve should 

 at once initiate degenerations, the morbid process and the re- 

 sulting loss of functional powers progressing until, "at a certain 

 stage, a stimulus, such as the interrupted current, while it fails 

 to affect the constrictor fibers, readily throws into action the 

 dilator fibers." 



