INNERVATION OF THE RESPIRATORY MOVEMENTS. 685 



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 noticeable changes in the respirations, 

 and corresponding to this fact experiment shows that stimula- 

 tion of certain portions of the cortex and midbrain gives distinct 

 effects upon the respiratory center. We must assume, therefore, 

 that this center is in connection with the sensory fibers of perhaps 

 all of the cranial and spinal nerves, and is influenced also by in- 

 tracentral paths passing from cerebrum to medulla, paths which 

 are efferent as regards the cerebrum, but afferent as regards the 

 medulla, As stated above, the effect of these sensory nerves 



Fig. 270. — To show the augmentation of the respiratory movements caused by stimulation of 

 the sciatic nerve. Experiment upon a rabbit. 



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 

 altogether or l^ecome slower and more feeble (Figs. 276 and 277) . 

 If in this, as in other similar cases, we assume that the two oppo- 

 site effects are produced by different nerve fibers we may speak of 

 sensory fibers which have a stimulating or augmenting effect, and 



