Theories and Experiments 247 



undertaken with the purpose of explaining the symptoms which 

 attack laborers working in compressed air; and as everyone has 

 observed that these symptoms occur at the moment of decom- 

 pression, Hoppe hoped to find their cause by studying death in 

 rarefied air. Here first is the summary of his experiments: 



A rat was subjected to a rapid decrease of pressure. Convulsions 

 occurred at about 50 mm. of mercury .... and death between 40 

 and 50 mm. On opening the thorax, .... there could be seen through 

 the walls of the vena cava, and the right auricle and ventricle, a 

 considerable quantity of gas which could be released by puncture .... 



In a cat ... . which died at about 40 mm., .... I found about 

 0.3 cubic centimeters of air in the vena cava and the right cavities 

 of the heart; there were a few bubbles of air in the left auricle. The 

 veins and the right heart were full of blood, the left heart almost 

 empty; the blood was completely liquid, the arteries contracted 

 spontaneously, the ventricles only under stimulation; the lungs were 

 empty of air and healthy; there was no rupture of vessels; the brain 

 was normal .... 



Two swallows died .... at a pressure between 125 and 120 mm.; 

 I found a few small bubbles of air in their blood 



In birds as in mammals, the blood of the left heart was bright 

 red, and consequently still contained oxygen .... 



Two frogs taken to the point of complete collapse were opened; 

 there was no gas in their hearts .... A slow-worm taken to a 

 pressure of 22 mm. swelled and remained motionless; then, a few 

 minutes after being returned to normal pressure, it seemed as well 

 as before. 



Summarizing: 



1. Birds die long before the point of effervescence of their blood; 

 mammals die at a pressure hardly above this point; amphibians do 

 not die even below this point; 



2. In warm-blooded animals, gas escapes in the interior of the 

 vessels as a result of rapid decrease of pressure. This is not true of 

 amphibians. 



F. Hoppe then asks himself whether death should be attributed 

 to this escape of the gases of the blood, or to the lack of oxygen 

 in the blood. It is very difficult to answer this question, he says: 

 "For, in the autopsy, the arterial blood is still bright red, and 

 very different from the blood of animals dying of asphyxia" (P. 

 67) ; an observation which is accurate, but due to an experimental 

 error which we shall demonstrate later. At any rate, the sudden 

 death seems to him to be certainly due to the obstruction of the 

 vessel by the gases liberated: 



The heart exerts upon its contents a pressure of 100 mm.; if the 

 air in the large venous trunks has a pressure of only 50 mm., it must 



