MOTOR NERVES AND MUSCULAR CONTRACTION. 253 



are distributed are almost reached. We must also remember 

 that this medulla is an extremely complex body. "Being so 

 complex," says Professor Foster, "it is naturally very unstable, 

 and, indeed, in its stability resembles putrid matter. Hence, 

 probably, the reason why the medulla changes so rapidly and 

 so profoundly after the death of the nerve." Viewed from 

 our standpoint, this suggests that, inasmuch as the vaso- 

 dilator fibers preserve their medulla until the vessels to which 

 they are distributed are nearly reached, they should degenerate 

 before the constrictors, which lose theirs early in their course. 

 And such would be the case did any such nerves exist in the 

 sciatic or brachial-plexus nerves or any nerve of the skeletal 

 muscular system. Indeed, were there any, their functional 

 activity would outlive that of the vasodilators, which is not 

 the case. If this fact is now considered in association with 

 the other features of this analysis, it seems to us to suggest 

 that the voluntary muscular system is not supplied with separate 

 vasoconstrictor nerves, and that the functions of the motor nerves 

 distributed to these muscles include that of vasoconstriction. 



Further evidence that this conclusion must represent the 

 actual state of things is afforded by the manner in which it 

 simplifies provided, of course, previous conclusions are like- 

 wise admissible the whole process which underlies voluntary 

 muscular activity, without in any way contradicting the data 

 sustained by experimental evidence. Indeed, vasoconstrictors 

 have never been found; an element of confusion is thus re- 

 moved which will probably enable us to ascertain the actual 

 effects of nerve-impulse on the voluntary muscular fibers and 

 their purpose. As to the vasodilators, another element of con- 

 fusion is removed through the fact that we now know from 

 data recorded in these pages that they need extend no farther 

 than the ultimate vascular subdivision, the walls of which con- 

 tain muscular elements: i.e., the arterioles. The fact that the 

 oxidizing substance of the blood-plasma reaches the muscular 

 elements themselves and can there exercise its life-sustaining 

 power and suddenly awaken activity also simplifies a very per- 

 plexing question. The capillaries which entwine the muscle- 

 fibers simply allow their plasma to ooze out through their 

 stomata, or endothelial-plate interstices, and to thus reach the 



