Sudden Changes in Pressure 857 



When we compare these few data with those which have already 

 been reported and in which the decompression was made very sud- 

 denly, we see that the physical phenomena amount to very little, 

 even when the rapidity of the experiment should have increased 

 their importance. We have already spoken of the expansion of the 

 intestinal gases; when the vacuum is made suddenly, they do not 

 have time to escape, and must contribute a part, though small, to 

 the distress of the animal. 



The pulmonary ecchymoses mean nothing, because we find 

 them in simple asphyxia, at normal pressure. 



The pulmonary hemorrhages are not a constant fact; besides, 

 we see them occur in certain cases when the pressure was dimin- 

 ished slowly; it is therefore difficult to ascribe them to the sud- 

 denness of the decompression. I should rather think that the sud- 

 denness caused the strange appearance of the lungs of the dog in 

 Experiment CLXXX, "The lungs are red in large patches, sinking 

 in water, but expanding completely after insufflation." 



This sort of fetal state seems to me to be due to a sort of suction 

 exercised in spots by the pressure of 7 cm. under which the animal 

 died. 



We saw in the historical part of this work that former authors 

 attached much importance to this phenomenon which some of them 

 considered constant and extending to the whole lung. We have 

 reported on this point the observations of Musschenbroeck, Guideus, 

 and Veratti. 



I myself have never seen the lungs of animals which were killed 

 by sudden decompression completely collapsed and heavier than 

 water in their entire mass. No doubt, as the ancients thought with- 

 out expressing themselves very clearly, when the weight of the air 

 is reduced to an amount below the strength of pulmonary elasticity, 

 the lung should collapse and a relative vacuum be made in the 

 pleura. But in the first place, this can happen only at pressures 

 lower than those at which animals die, because the pulmonary 

 elasticity of a dog, even in the condition of maximum inspiration, 

 even added to the negative pressure, does not go beyond 5 or 6 

 centimeters of mercury; this value is still less for smaller animals. 

 Finally, even supposing this empty space exists in the pleura, it is 

 evident that, when normal pressure is reestablished, the lungs will 

 be retracted to their original position, or the ribs would be broken 

 under the atmospheric pressure, as I formerly showed experi- 

 mentally; so that, even if this phenomenon occurred, there will be 

 no trace of it in the autopsy. For the pulmonary retraction to 



