230 NERVOUS SYSTEM. 



points to the fact that its action is not direct, but reflex, and 

 is due to an impression conveyed to the nerve-centres. 



If the central ends of the nerves be galvanized, the press- 

 ure in the arteries diminishes little by little, until it may be 

 reduced to one-half or two-thirds of the pressure before the 

 irritation was applied. This low pressure continues so long 

 as the interrupted current is applied ; but when the galvani- 

 zation is arrested, it gradually returns to the normal stand- 

 ard. These phenomena are observed in all the large arterial 

 trunks. The length of time required to produce the great- 

 est diminution in the pressure is somewhat variable, but the 

 experimenters have never seen it reach its minimum before 

 fifteen pulsations of the heart. 



" The diminution in the pressure is attended with a re- 

 duction of the pulse in the instances in which the depressor- 

 nerve only has been divided. The irritated nerve is isolated 

 in a manner so complete that we cannot fear the passage of 

 the exciting current in the trunk of the pneumogastric. The 

 changes in the number of pulsations persist even when the 

 pneumogastric has been excited by the side where the irri- 

 tation has been applied, from the point where the superior 

 laryngeal is given off to the point where the pneumogas- 

 tric enters the thoracic cavity. 



" From the foregoing it is evident that the changes tak- 

 ing place in the number of pulsations are due to excitation 

 of the depressor-nerve. If we study attentively the progress 

 of the cardiac pulsations during the excitation, we observe 

 always that the most considerable reduction takes place at 

 the beginning of the experiment ; that is to say, at the 

 moment when the blood-pressure descends from its normal 

 standard to the lowest point. When the pressure is com- 

 pletely depressed, the pulse is accelerated again and even 

 reaches almost completely the numbers presented before the 

 oscillations. "When the irritation ceases, after a shorter 

 or longer period, the heart generally beats more rapidly 

 than before the irritation, and this during all the time that 



