MEDULLA OBLOXGATA. 443 



cedes death, is an irregular, hesitating respiration, which sometimes 

 attracts the attention of the physician, even before the remaining 

 cerebral functions are seriously impaired. These phenomena de- 

 pend on the connection between the respiratory movements and the 

 reflex action of the medulla oblongata. 



We have now, in studying the functions of various parts of the 

 cerebro- spinal system, become familiar with three different kinds of 

 reflex action. 



The first is that of the spinal cord. Here, there is no proper 

 sensation and no direct consciousness of the act which is performed. 

 It is simply a nervous impression, coming from the integument, 

 and transformed by the gray matter of the spinal cord into a motor 

 impulse destined for the muscles. This action will take place after 

 the removal of the hemispheres and the abolition of consciousness, 

 as well as in the ordinary condition. The respiratory action of the 

 medulla oblongata is of the same general character ; that is, it is 

 not necessarily connected with either volition or consciousness. 

 The only peculiarity in this instance is that the original nervous 

 impression is of a special character, and its influence is finally 

 exerted upon a special muscular apparatus. Actions of this nature 

 are termed, par excellence, reflex actions. 



The second kind of reflex action takes place in the tuber annu- 

 lare. Here the nervous impression, which is conveyed inward 

 from the integument, instead of stopping at the spinal cord, passes 

 onward to the tuber annulare, where it first gives rise to a con- 

 scious sensation; and this sensation is immediately followed by a 

 voluntary act. Thus, if a crumb of bread fall into the larynx, the 

 sensation produced by it excites the movement of coughing. The 

 sensations of hunger and thirst excite a desire for food and drink. 

 The sexual impulse acts in precisely the same manner ; the percep- 

 tion of particular objects giving rise immediately to special desires 

 of a sexual character. 



It will be observed, in these instances, that in the first place, 

 the nervous sensation must be actually perceived, in order to pro- 

 duce its effect; and in the second place that the action which 

 follows is wholly voluntary in character. But the most important 

 peculiarity, in this respect, is that the voluntary impulse follows 

 directly upon the receipt of the sensation. There is no intermediate 

 reasoning or intellectual process. We do not cough because we 

 know that this is the most effectual way to clear the larynx ; but 

 simply because we are impelled to do so by the sensation which is 



