248 Historical 



be compressed a third of its volume to enter the arteries; the result is 

 a great slackening of the circulation. If this slackening, joined to 

 the small quantity of oxygen contained in the blood and the unequal 

 power of the right and the left heart, can cause death, it can be only 

 an instantaneous death. This death can be caused only by the 

 obstruction of the capillaries of the lungs by bubbles of air, whence 

 comes the stoppage of the circulation. 



He does not limit himself to this theoretical demonstration, and 

 tries to prove experimentally that it is not the lack of oxygen, But 

 the decrease of the pressure which kills animals placed under the 

 bell jar of the pneumatic machine. To make this proof, he uses a 

 method which, long before I knew the work of Hoppe, one of the 

 last I found in my bibliographical research, I frequently used, and 

 from which, as will be seen, I have drawn conclusions diametri- 

 cally opposite to his. It will be interesting to discuss the reason 

 for these differences; but this is not the place to do so. 



At any rate, Hoppe said to himself: if it is the decrease of pres- 

 sure which brings death, and not the lack of oxygen, death will 

 necessarily occur at the same pressure, even if pure oxygen is 

 used: 



A guinea pig fell in convulsions at 77 mm.; pure oxygen was 

 admitted into the b'ell, and it rose at once. When the pressure had 

 been lowered again, it experienced the same symptoms at 75 mm.; sec- 

 ond admission of oxygen, third lowering of pressure: symptoms at 75 

 mm.; another admission of oxygen, collapse at 75 mm. Return to 

 normal pressure; the animal survived. (P. 69.) .... 



So the symptoms of sudden asphyxia came at the same pressure, 

 whether the animal was in air or in oxygen. 



From this he draws the definite conclusion that the cause of 

 death lies in the appearance of free gases; the moment of their 

 escape varies with "the pressure, the temperature of the animal, 

 the power of absorption and the affinity of the blood for gases, and 

 the quantity of blood corpuscles". 



The important researches of M. Fernet 83 this same year brought 

 to the question a new element which, during later discussions of 

 the cause of mountain sickness, seemed to support mistaken 

 theories. 



Ever since the early experiments of Robert Bojde, it had been 

 known that gases in considerable quantities are present in the 

 blood. More recent chemists, particularly Magnus 81 in 1837, had 

 shown that oxygen forms a very large proportion of the gases. 

 From these experiments physiologists had been led to conclude 

 that respiration is only a simple exchange of gases between the 



