INNERVATION OF THE RESPIRATORY MOVEMENTS. 701 



or inhibitory apnea. 1 1 is generally stated* that after section of the 

 vagi it is more difficult than in the normal animal to produce apnea 

 by vigorous artificial respiration, so doubtless in this last proce- 

 dure, as usually carried out with a bellows, the rapid stimulation 

 of the inhibitory fibers of the vagus by the expansion of the lungs 

 facilitates the production of a true or chemical apnea. In the pre- 

 ceding paragraphs evidence has been given to show that the normal 

 stimulus to the center is due to the presence of CO 2 , and it fol- 

 lows logically that the more complete removal of this gas by venti- 

 lation of the lungs should be considered as the chief cause of true 

 apnea. Experimentally, this view is well borne out by an old 

 observation of Berns, according to which a condition of apnea 



Fig. 281. To show the recovery from apnea. The animal (rabbit) had been venti- 

 lated with a bellows and thrown into a condition of apnea shown at the beginning 

 of the record. The respirations returned first as feeble movements which gradually in- 

 creaaed to the normal. (Dawson.) 



in a rabbit may be cut short at any moment by a blast of CO 2 

 sent into the lungs, a blast of air having no such effect. This 

 observation is further supported by experiments by Mossof upon 

 men, in which he shows that apnea cannot be produced by inflation 

 with carbon dioxid. This author designates the condition of 

 diminished CO 2 in the blood as acapnia. According to this 

 terminology, true apnea is due to a condition of acapnia. 



Much other work has tended to strengthen the general view 

 that a certain tension or pressure of CO 2 in the blood is neces- 

 sary to stimulate the respiratory center, and that if the CO 2 is 

 washed out to a certain point by unusual ventilation of the 

 lungs (condition of acapnia) , then the respiratory center ceases to 



* See Head, "Journal of Physiology," 10, 1, and 279, 1889. 



ie bi< " 



t Mosso, "Archives italiennes de biologic," 40, 1, 1903. 



