698 PHYSIOLOGY OF RESPIRATION. 



the amount of carbon dioxicl. It follows logically that the more 

 complete removal of this gas by ventilation 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, accord- 

 ing to which a condition of apnea in a rabbit may be cut short 

 at any moment by a blast of COo sent into the lungs, a blast of 

 air having no such effect. This observation is further supported 

 by experiments by Mosso* upon men, in which he shows that 

 apnea cannot be produced by inflation with carbon dioxid. This 

 author designates the condition of diminished COo in the blood 



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- 

 creased to the normal. — (Dawson.) 



as acapnia. According to this terminology, true apnea is due to 

 a condition of acapnia. 



Increased rapidity or depth of breathing tends to reduce the 

 concentration of CO2 in the alveolar air and, consequently, the 

 pressure of COo in the arterial blood. When this pressure falls be- 

 low a certain level in the normal animal (19 to 24 mms.,Zuntz), the 

 respiratory center is not stimulated. There is a condition of com- 

 plete apnea. Smaller reductions in carbon dioxid pressure cause 

 partial apnea, that is, a reduction in the rate or amplitude of the 

 respirations. Voluntary forced respirations in man maintained for 

 some minutes will produce a similar condition. According to the 

 interesting account given by Haldane and Poulton f an apnea may 

 be produced in this way which will last for 100 to 150 seconds, and 

 before the individual begins to breathe again he may become 



* Mosso, "Archives italiennes de biologie," 40, 1, 1903. 



t Haldane and Poulton, "Journal of Physiology," 37, 390, 1908. 



