1913] Henry H. Janeway and Ephraim M. Ezving 405 



stopped at the end of the experiment, the period of apnea lasted 

 only one or two minutes, so that no death resulted directly from 

 asphyxia dependent in turn upon acapnia. The absence of a pro- 

 longed period of apnea is explained by the fact that the effect of ether 

 was not added to that of morphin. 



With a tJiird series of animals the experiments just described 

 were duplicated, with the exception that the carbon-dioxide content 

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

 The conservation of the carbon dioxide was accomplished by insert- 

 ing 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 the small 

 amount of air and carbon dioxide lost from the animal's trachea, 

 carbon dioxide was administered from a tank into the rubber bag, 

 where it mixed with air drawn in from the trachea. In these ex- 

 periments the animals went into the same degree of shock in two 

 or three hours as those of the second series, in which the carbon- 

 dioxide content of the blood was diminished to 40 per cent. of the 

 original volume. One animal died on the table just before the com- 

 pletion of the experiment, the others lived for from one to three 

 days. Blood-pressure changes in the two series were similar but a 

 characteristic of the experiments, in which the carbon-dioxide con- 

 tent was kept at or a little above the normal, was a less rapid and 

 weaker heart-beat than that observed when the carbon-dioxide con- 

 tent was diminished. 



No other conclusions can be drawn from the experiments of 

 Series i and 2 than that the reduction in the carbon-dioxide content 

 of the blood was not an important factor in the causation of shock 

 produced by hyper-respiration, and that in shock so produced, the 

 essential factor was an interference with the venous return to the 

 heart. 



In the fourth series of experiments the effects of aerating and 

 handling 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, the content of carbon dioxide was slightly 



