DEPBESSOK-NERVE. 231 



is occupied in the return of the pressure to the normal stand- 

 ard. This observation in itself refutes the idea that the 

 diminution in the pressure may depend upon the diminished 

 number of pulsations. If the reduction in the rate of the 

 pulse produced a diminished pressure, it should be increased 

 when the pulsations of the heart become accelerated. 



" The manner in which the pulse is reduced leads to the 

 supposition that it is due to a reflex action of the pneunao- 

 gastric. 



"It was easy to verify this last opinion, and we have 

 been able to confirm it by first cutting the pneumogastrics 

 on both sides, and afterward irritating the central end of the 

 depressor-nerve. In this case, the pressure fell to 0.62, 0.55, 

 etc., while the number of pulsations remained the same, or 

 at least oscillated very slightly above and below the number 

 observed before the irritation." 



The above extract from the observations of Cyqn shows 

 two important points : 



First, galvanic stimulation of the central extremities of 

 the divided depressor-nerves reduces the number of pulsa- 

 tions of the heart by a reflex action ; the impression being 

 conveyed to the nerve-centres by the depressor-nerves, the 

 force acting directly upon the heart being transmitted through 

 efferent filaments in the trunk of the pneumogastric. 



Second, the reduction in the pressure of blood in the 

 larger arteries is independent of the efferent filaments of the 

 pneumogastric, and bears no relation to the reduction in the 

 number of cardiac pulsations. 



It now remains to explain, if possible, the mechanism of 

 the reduction in the arterial pressure. This question is 

 treated by Cyon by the method of exclusion. The diminu- 

 tion in the pressure followed galvanization of the central ex- 

 tremities of the depressor-nerves, even when the heart was 

 removed from its influence by section of both pneumogas- 

 trics in the neck, and when all the voluntary movements 

 and the movements of respiration were abolished by poison- 



