Chapter VII 



EFFECTS OF SUDDEN CHANGES IN 

 BAROMETRIC PRESSURE 



Hitherto, I have spoken. only of the phenomena following grad- 

 ual changes in the amount of the barometric pressure, which are, 

 as we have seen, phenomena of the physico-chemical type, result- 

 ing from the presence in the blood of larger or smaller quantities 

 of oxygen. But it is only in these conditions of gradual change 

 that I could be brought to deny the effect of the pressure as a direct 

 agency, of the physico-mechaniccu 1 type. Of course it may be dif- 

 ferent when we are dealing with sudden and considerable changes. 

 The experiments reported in this chapter were intended to settle 

 this question. 



Subchapter I 

 EFFECT OF SUDDEN INCREASES IN PRESSURE 



This part of the work will not be long. The sudden increase of 

 pressure seems to have no appreciable effect on animals. 



At first, when it was a matter of animals previously subjected 

 to a very low pressure, like that discussed in Chapters I and III, 

 the restoration of normal pressure had no apparent ill consequence. 

 But on the contrary, when the decompression was very great, its 

 favorable effect appeared immediately, and the animal returned at 

 once to a normal state. We could see it then perceptibly "deflate," 

 especially in the case of a herbivorous mammal, as a result of the 

 return to their original volume of the intestinal gases, which the 

 decompression had expanded. 



The experiments on sudden increase of pressure were made on 

 rats or birds placed in the Seltzer water receiver. This receiver 



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