CONTRACTILITY OF THE ARTERIES. 251 



has shown, by a beautiful series of experiments, which will 

 be more particularly alluded to on the subject of secretion, 

 that galvanization of what he calls the motor nerve of a 

 gland dilates the vessels, largely increases the supply of blood, 

 and induces secretion ; while galvanization of the sympathetic 

 filaments contracts the vessels, diminishes the supply of blood, 

 and arrests secretion. The pallor of parts exposed to cold, 

 and the flush produced by heat, are due, on the one hand, to 

 contraction, and on the other to dilatation of the small arter- 

 ies. Pallor and blushing from mental emotions are examples 

 of the same kind of action. 



The ulterior effects on nutrition, which result from dila- 

 tation of the vessels of a part, are of great interest. When the 

 supply of blood is much increased, as in section of the 

 sympathetic in the neck, nutrition is exaggerated, and the 

 temperature is raised beyond that of the rest of the body. 



The idea, which at one time obtained, that the arteries 

 were the seat of rhythmical contractions, which had a favor- 

 able influence on the current of blood, is entirely erroneous. 1 

 It is hardly necessary to repeat that the prime cause of 

 the arterial circulation is the force of the ventricles. "We 

 have seen that the elasticity of the arteries produces a flow 

 during the intervals of the heart's action, and the question 

 now arises whether the force thus exerted is simply a re- 

 turn of the force required to expand the vessels, which has 

 been borrowed, as it were, from the heart, or is something 

 superadded to the force of the heart. The experiment of 

 Marey, already alluded to, settles this question. When 

 water was forced in an intermittent current into two tubes, 

 one elastic and the other inelastic, but discharging by open- 

 ings of equal size, by far the greater quantity was discharged 

 by the elastic tube. A little reflection will show how the 



1 Schiff has noticed rhythmical contractions in the superficial arteries of the 

 ear in the rabbit, and some other animals ; but this phenomenon is excep- 

 tional, and the movements do not appear to favor the current of blood. 

 ( MILNE-EDWARDS, Physiologic tome, iv., p. 217.) 



