MOTOR NERVES AND MUSCULAR CONTRACTION. 247 



rapid flow; while the veins are for the time being, as long 

 as active functions continue, transformed into arterial chan- 

 nels. Briefly, more arterial blood means more work. As we 

 will see later on, this is the only process through which the 

 potential of any organ i.e., its latent power to do work is 

 maintained and its functional activity awakened when required. 

 Whether the structures involved be muscular, hepatic, gastric, 

 renal, cerebral, splenic, etc., the exciting factor of activity is 

 always shall we say blood? No; all this evidence emphasizes 

 the fact that the oxidizing substance is the main factor of all 

 functional processes, and that the red corpuscles are but carriers 

 of oxygen intended to sustain the plasma's efficiency as an oxidiz- 

 ing body. We have seen that Salkowski was also led, but by 

 chemical methods, to deny the red corpuscles the all-important 

 role now ascribed to them. 



THE MOTOR NERVES AND THEIR ROLE IN MUSCULAR 

 CONTRACTION. We must now transfer our attention to the 

 "vasoconstrictor" side of the question. The sciatic nerve is 

 thought to be supplied with vasodilator and vasoconstrictor 

 fibers. Division of this nerve causes the usual widening of 

 the arteries, while electrical stimulation of the peripheral 

 nerve-end causes contraction of the dilated arteries. This 

 coincides with the experimental results of section of the cer- 

 vical sympathetic, the splanchnic, etc., already given. "But 

 sometimes a different result is obtained," says Foster, "on 

 stimulating the divided sciatic nerve: the vessels of the foot 

 are not restricted, but dilated perhaps widely dilated": a 

 phenomenon which leads him to conclude "that the sciatic 

 nerve (and the same holds good for the brachial plexus) con- 

 tains both vasoconstrictor and vasodilator fibers," and to in- 

 terpret the varying results as due "to variations in the relative 

 irritability of the two sets of fibers." 4 These remarks are only 

 intended by their author to convey, not a personal conclusion, 

 but an inferential deduction based on what testimony the ex- 

 periment referred to affords as to the existence, in the sciatic 

 and brachial plexuses, of both constrictor and dilator fibers. 

 It is the value of the testimony itself, and not the author's 

 deduction, therefore, that we are analyzing. 



* The italics are our own. 



