Summary and Discussion 345 



Cloquet 4 has shown, are immobilized in a certain state of expan- 

 sion, because an equilibrium has been established between the 

 pressure of the expiratory muscles and the elasticity of the intra- 

 pulmonary gases which the closed glottis prevents from escaping, 

 the original density of these gases should be important. If they 

 are rarefied, the state of equilibrium will occur only with a 

 stronger contraction, or a smaller expansion of the thorax, and this 

 situation may be unfavorable to the phenomena of maximum ef- 

 fort,. But the effect, in any case, should not be of great impor- 

 tance. 



Musschenbroeck had given a very ingenious explanation of the 

 death of animals in a vacuum. He had found their lungs "small, 

 flabby, solid (page 198), specifically heavier than water," and he 

 had considered that the death is the result of the stoppage of the 

 circulation which this collapse should produce; the same fact was 

 noted by the Dutch physiologists (page 202) , who interpreted it 

 a little differently. But these explanations cannot, however, be 

 applied to disturbances and death in an air which is much rare- 

 fied but still far from a perfect vacuum. Cigna long ago com- 

 mented that respiration should continue under these conditions, 

 as long as "the air is dense enough to expand the lungs by its 

 pressure"; but for that, it is sufficient "that this pressure should 

 overcome the resistance offered by the contractile force of the 

 lungs, for there is no thoracic air to increase this resistance, and 

 this pressure hardly exceeds that of two inches of mercury" (page 

 207). 



It could not be better stated, and Cigna was replying in ad- 

 vance, without knowing it, to those who would later give an im- 

 portant part in mountain sickness to the tendency of the lungs to 

 retract under a lessened density of the intra-pulmonary air. Their 

 force, that is, their elasticity, is equal to only a few centimeters 

 of mercury, as Cigna had said. Therefore only under a still lower 

 pressure could the lungs separate from the thorax wall, making 

 a vacuum in the pleura. The supposed effect is therefore abso- 

 lutely nil. 



Pravaz fell into a similar error when he said that "in mountain 

 air, respiration is mechanically restrained in its extent by the lack 

 of elasticity in the atmosphere which presses the interior of the 

 lungs" (page 239). His opinion is subject to the same objections. 

 But at least it has some appearance of probability, whereas I can- 

 not understand what made A. Vogt say that "the diminished at- 

 mospheric pressure assists greatly in the expansion of the thoracic 

 cavity, and thereby facilitates respiration" (page 237) . 



