1026 Summary and Conclusions 



ment of the lower animals, frog tadpoles, the larvae of insects, kept 

 for a long time under tensions of compressed oxygen between 21 

 and 100, show very clearly that even if there is an increase in 

 nutritive processes, there is no better general condition; far from 

 it. Beginning even with 80, the fatal effect of the oxygen is evi- 

 dently felt. The same thing is even more true for germinations, 

 which never take place better than under normal pressure. 



When I had studied this point, I could not help being interested 

 in the modifications caused by compressed air in circulation and 

 respiration, modifications so often analyzed by doctors. Following 

 many other observers, I noted the decrease in the number of pulsa- 

 tions and the increase in the maximum pulmonary capacity: I 

 found that the quantity of air (in volume) which passes through 

 the lungs during a given time does not change noticeably in com- 

 pressed air: this point had not been directly investigated before 

 me; I should say that, according to G. Liebig, it would decrease 

 a little (in the ratio of 118 to 100). 



The most interesting fact which this part of my researches fur- 

 nished me is the proof that the greater capacity of the lungs is 

 due to the mechanical action of the compression upon the intes- 

 tinal gases (p. 768) . It has another result of lessening the varia- 

 tions of the intrathoracic air pressure during the acts of inspira- 

 tion and expiration. Finally, I was the first to measure directly 

 the arterial pressure under compression, and to show that it is 

 considerably increased by the mechanical action of the pressure. 



Up to now I have been rather severe against the explanations 

 which emphasized the mechanical side of the pressure and have 

 dwelt upon these new observations. But, as I have often said, 

 from this point of view, the pressure can act only on the gaseous 

 reservoirs; it does so for the intestine, which is like a closed bladder, 

 whose volume diminishes following Mariotte's Law, the lung hav- 

 ing to follow the diaphragm which drops more; it does so for the 

 thorax, which would be crushed if the tracheal opening did not 

 exist, and which would not be affected at all if this opening were, 

 as it is not, sufficiently wide. 



But the relative intensity of this action of the pressure continues 

 to diminish with the amount of the compression; and that is easily 

 understood, for if the intestine loses, in passing from one to two 

 atmospheres, half of its volume, it diminishes only a fourth more 

 in passing from two to four. Furthermore, the increase of the 

 thoracic capacity can represent only a part of the reduction of the 

 volume of the intestine, because the walls of the abdomen fill up 



