634 



PHYSIOLOGY OF RESPIRATION. 



experience, since everyone 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 t ion 



morliilla Ac cfnforl ohrkx^ fViA by stimulation of the sciatic nerve. Ex- 



tneduiia. AS stated above, tne periment upon a rabbit. 



effect of these sensory nerves 



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



Fig. 256. To show the inhibition of the respiratory movements in a rabbit due to 

 stimulation of the central end of the vagus. The respiratory movements in this case, 

 before and after stimulation, were forced, owing to the fact that both vagi were cut. 



be changed together with an increased or decreased amplitude, the 

 inspirations and expirations may each be increased, or one phase 



