688 



PHYSIOLOGY OF RESPIRATION. 



activity of the respiratory center has been referred by some authors 

 to reflex stimulation of the center by sensory impulses arising in 

 the respiratory muscles themselves. To exclude this possibility 

 Winterstein curarized an animal to immobilize the respiratory 

 muscles, and then divided the phrenic nerve and connected its 

 central stump with a galvanometer. Under these conditions the 

 galvanometer recorded rhythmic action currents, which demon- 

 strated that the respiratory center was sending out rhythmic 

 discharges of nerve impulses. 



Reflex Stimulation of the Center. According to the results 

 of numerous observers, stimulation of any of the sensory nerves 

 of the body may affect the rate or the amplitude of the respiratory 

 movements. This experimental result is confirmed by our own 

 experience, since every one must have noticed that the respiratory 

 movements are readily affected by strong stimulation of the cutane- 



ous nerves a dash of cold water, 



for example as well as through 

 the nerves of sight and hearing. 

 In addition, emotional states are 

 apt to be accompanied by notice* 

 able changes in the respirations, 

 and corresponding to this fact 

 experiment shows that stimula- 

 tion of certain portions of the cor- 

 tex and midbrain gives distinct 

 effects upon the respiratory cen- 

 ter. We must assume, therefore, 

 that this center is in connection 

 with the sensory fibers of per- 

 haps all of the cranial and spinal 

 nerves, and is influenced also by 

 intracentral paths passing from 

 cerebrum to medulla, paths which 

 are efferent as regards the cere* 

 brum, but afferent as regards the 

 medulla. As stated above, the 

 effect of these sensory nerves 



upon the activity of the respiratory center is varied; the rate may 

 be changed together with an increased or decreased amplitude, the 

 inspirations and expirations may each be increased, or one phase 

 may be affected more markedly than the other. In general, how- 

 ever, experimental stimulation of a sensory nerve trunk which con- 

 tains cutaneous fibers gives one of two effects : either a stimulating 

 action, manifested by quicker, stronger inspirations and active ex- 

 pirations, or an inhibitory effect, in which the respirations cease 



Fig. 276. To show the augmenta- 

 tion of the respiratory movements caused 

 by stimulation of the sciatic nerve. Ex 

 periment upon a rabbit. 



