236 THE ADRENAL SYSTEM AND VASOMOTOR FUNCTIONS. 



ends nearer together. When repeated shocks are given, wave 

 follows wave of nervous impulse, muscle-impulse, and visible 

 contraction; but the last do not keep distinct; they are fused 

 into the continued shortening which we call tetanus/' 



The last word, "tetanus," stands as the highest expression 

 of a rapid succession of nervous impulses; but, viewed from our 

 standpoint, this succession of impulses can as readily produce 

 successive variations of vascular caliber, and give rise to pre- 

 cisely the phenomena witnessed, by admitting the oxidizing sub- 

 stance of the blood-plasma into the fine, "membranous tubes." 

 The shock experienced when the current is turned "on" or "off" 

 further suggests that the latter process is the true one. "The 

 mere passage of a constant current of uniform intensity 

 through a nerve does not, under any circumstances," says 

 Professor Foster, "act as a stimulus generating a nervous im- 

 pulse; such an impulse is only set up when the current either 

 falls into or is shut off from the nerve. It is the entrance 

 or the exit of the current, and not the continuance of the 

 current, which is the stimulus." . . . "It is the sudden 

 change from one condition to another, and not the condition 

 itself, which causes the nervous impulse." 2 



The confusion that attends prevailing views as to the 

 manner in which muscular tissue is physiologically caused to 

 contract is readily accounted for when, in the light of the 

 newer conceptions outlined in the last chapter, we analytically 

 dissociate the various causal elements of muscular activity. 

 Indeed, we have seen that various phenomena ascribed to the 

 sympathetic system belonged to the domain of the suprarenal 

 glands, i.e., to the newer system described; we are again 

 brought to realize that in all organs certain functions must 

 likewise, and for the same reasons, be disconnected from 

 others as regards their immediate purpose in the tissues. 

 Thus, the fact that the muscle-impulse, which "travels from 

 each end-plate in both directions to the end of the fiber, where 

 it appears to be lost," is at present considered as an inherent, 

 though causal, element of the "explosive decomposition of 

 material, etc.," through its activity as a physiological stimulus. 



8 All italics are our own. 



