232 STUDIES IN ADVANCED PHYSIOLOGY. 



its accustomed place by the drop of the body and goes 

 crushing through the medulla. As the respiratory center 

 lies just at this point it is destroyed, and an immediate par- 

 alysis of all the muscles of respiration ensues. In conse- 

 quence of this the criminal dies by suffocation, not being 

 able to get more air. Such a displacement of the neck is 

 called ' 'breaking of the neck. ' ' It is tolerably easy to locate 

 this point by introducing sharp-pointed needles into the 

 medulla. A point is soon found which, upon being pierced 

 results at once in a respiratory paralysis, and the position 

 of this point in the floor of the fourth ventricle has just been 

 noted. We must look to this center, therefore, as the source 

 of our respiratory impulses. 



The question at once arises, what causes this center to 

 send out impulses along the motor nerves just mentioned? 

 A few simple experiments serve to materially clarify this. 

 If an individual breathes very rapidly and deeply, and so 

 gets into his lungs, and consequently into his blood, in- 

 creased amounts of oxygen, the center becomes quiescent, 

 and for a little while there is no tendency or temptation to 

 breathe. This might seem to show that it is the absence 

 of sufficient oxygen which normally stimulates the center, 

 for as soon as the blood is richly supplied with oxygen by 

 taking repeated deep breaths, the center becomes inactive. 

 On the other hand, if the supply of air be cut off and the 

 blood in the body becomes strongly venous, the center be- 

 comes more and more irritable, sends out stronger and 

 stronger impulses to breathe, until finally the impulses be- 

 come so strong and scattered as to produce convulsions. In 

 such venous blood there is still a little oxygen, but much 

 carbon dioxide, and the opinion has been advanced that it 

 is not so much the lack of oxygen as it is the presence of 

 carbon dioxide that stimulates the center. Other physiol- 

 ogists, to reconcile both views, combine the two notions 

 and state that the absence of oxygen, as well as the pres- 

 ence of carbon dioxide, serve to irritate and stimulate the 

 center to action. It seems, however, difficult to conceive 



