MOTOR NERVES AND MUSCULAR CONTRACTION. 255 



but little elasticity, and, when it is compressed by the muscular 

 layer encircling it, it happens that the lowest limit of its elas- 

 ticity is surpassed and that, in order to accommodate itself to 

 the restricted space reserved for it, it forms folds. It is for 

 this reason that a transverse section causes it to appear as 

 if festooned, while longitudinal sections of these small arteries, 

 owing to folds formed during muscular retraction, give the 

 appearance of longitudinal strias." From our point of view 

 this is subject to another interpretation. Indeed, this festoon- 

 ing in longitudinal folds, observed to a limited extent in all 

 small arteries, coupled with the effects of muscular retrac- 

 tion, seems to us to distinctly point to the mechanical process 

 through which efficient changes in the caliber of the arterioles 

 are insured. 



The impulse, we have seen, travels from the end-plate 

 toward the extremities of the muscular fiber and the muscle 

 contracts, according to our view, as the result of dilation of 

 the arterioles. While the sudden onset of oxidizing plasma, 

 by suddenly increasing the production of chemical energy, 

 which in turn is converted into contractile energy, accounts for 

 the latter, it does not account for the "voluntary" element of 

 the process, nor for the wonderful precision which character- 

 izes muscular movements those of the fingers, for instance. 

 Indeed, myosinogen plus the oxidizing substance must be con- 

 sidered if our doctrine prevails as the only source of work, 

 but not as the intermediary through which the volition (con- 

 scious or unconscious) implied by the word "voluntary/ 5 and 

 the functional control that this implicates, is obeyed. In 

 other words, it constitutes what in the locomotive is repre- 

 sented by the combination of fire, water, and steam, but it 

 does not represent the throttle-valve, which is subject to the 

 will of the engineer. His "voluntary" act, transmitted through 

 the lever, regulates the quantity of steam admitted into the 

 cylinder in which heat is transformed into work. In the 

 muscle each "fine, transparent, membranous tube" is a cylin- 

 der, but one in which the conversion of energy into work is 

 the result of a local process in which myosinogen plus the 

 oxidizing substance are the sources of energy. The throttle- 

 valve is obviously the arteriole, but so located as to admit as 



