Factors of Excessive Artificial Respiration. 133 



temporarily stopped or permanently stopped at the end of the 

 experiment the period of apnea lasted only one or two minutes, 

 so that no death resulted directly from acapnia. The absence 

 of a prolonged period of apnea is explained by the fact that the 

 effect of ether was not added to that of morphine. 



With a third series of animals, the experiments just described 

 were duplicated with the exception that the C0 2 content of the 

 blood was maintained at its normal level, or slightly above it. 

 The conservation of C0 2 was accomplished by inserting a large 

 rubber bag, to act as a reservoir, between the suction pump and 

 the force pump, thus creating an almost perfectly closed circuit; 

 the dog thus rebreathed expired air. To replace a small amount 

 of air lost from the animal's trachea, C0 2 was fed from a tank into 

 the rubber bag where the latter was diluted with air drawn in from 

 the trachea in smaller quantities than that amount lost through 

 this route. In these experiments the animals went into the same 

 degree of shock in 2 or 3 hours as those of Series II in which the C0 2 

 content of the blood was diminished to 40 per cent, of the original 

 volume. One animal died on the table just before the experiment 

 closed, the others lived one to three days. Blood pressure changes 

 in the two series were similar, but a characteristic of the experiment 

 when the C0 2 was kept high, was the slow, strong heart beat, in 

 place of the rapid, weak pulse observed when the C0 2 was di- 

 minished. Conclusions drawn from Series II and III can only 

 be that the reduction in the C0 2 content of the blood is not the 

 important factor in the production of shock by hyper-respiration, 

 but that in the shock so produced, the essential factor is an in- 

 terference with the venous return to the heart. 



In the fourth series of experiments the effects of aeration and 

 handling of the intestines were studied. A celluloid window was 

 placed in the abdominal wall, and a stream of warm, moistened 

 air was passed over the intestines for a period of three hours. 

 During this procedure the animals breathed normally, the blood 

 pressure was 163 mm. Hg, C0 2 content was normal, and there was 

 no evidence of shock. The celluloid was then removed, the 

 intestines spread out, and the aeration continued. After 45 

 minutes the C0 2 determination showed 38.8 volume per cent., 

 and blood pressure was 153 mm. Hg. The intestines were then 



