708 PHYSIOLOGY OF RESPIRATION. 



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- 

 creased to the normal. (Dawaan.) 



in a rabbit may be cut short at any moment by a blast of CO2 

 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 C0 2 in the blood as acapnia. According to this 

 terminology, true apnea is duetto a condition of acapnia. 



Increased rapidity or depth of breathing tends to reduce the 

 concentration of C0 2 in the alveolar air and, consequently, the 

 pressure of C0 2 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 Poultonf 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 

 very blue in the face, owing to the using up of the oxygen in the 

 lungs. In addition to the factors discussed above, namely, reflex 



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



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



