260 THE ADRENAL SYSTEM AND VASOMOTOR FUNCTIONS. 



within the latter, it forms the folds or "festooning" described 

 by Eanvier. Viewed from our standpoint, however, these 

 longitudinal folds play a very important part in the whole 

 mechanical process described, since it is upon variations of 

 their outline that the adjustment of the lumen of the vessel 

 mainly depends. Mere dilation of a circular vessel, of course, 

 involves an increase in the diameter of the stream passing 

 through it; but, if numerous folds that project into that 

 stream are simultaneously withdrawn by being leveled out, it 

 is evident that the free space within the vessel will be vastly 

 increased, and that a much greater range between dilation and 

 contraction will thus be available. 



That such is the process through which a slight variation 

 of the peripheral pressure exerted by the muscular layer will 

 cause a relatively larger variation of the amount of blood to 

 pass through the vessel seems very probable, since it satisfies 

 all mechanical needs. As long as the characteristic impulse- 

 wave of a fixed degree of muscular contraction persists, the 

 vessels are simultaneously adjusted to the needs of this par- 

 ticular degree of contraction and allow just the necessary 

 amount of blood i.e., oxidizing plasma to pass. 



Returning now to the contradictory results of stimulation 

 of the sciatic after section of that nerve, an important feature 

 must be referred to, which, if considered before, would have 

 but introduced confusion in the inquiry: i.e., the fact that 

 stimulation of this nerve immediately after section may either 

 be followed by dilation or constriction. Laryngologists are 

 quite familiar with the fact that one strength of current will 

 cause adduction of the vocal bands, i.e., of their muscles, 

 while another strength will cause the opposite condition ab- 

 duction, when the recurrent laryngeal nerve is cut and stim- 

 ulated. That the same controlling factor must prevail in the 

 case of the sciatic is very probable, if, as we have suggested, 

 the rhythm of the impulse-wave determines the degree of mus- 

 cular contraction. The certainty with which dilation is pro- 

 duced when the nerve is stimulated "some days after division" 

 is a phenomenon of another sort. The electric current does 

 not, like a normal nerve-impulse, select a physiological path; 

 it simply utilizes the channels that offer the least resistance. 



