﻿AIR AND LIFE. 55 



Even at the bottom of tbe deepest mines, although pressure is appreci- 

 ably increased, this increase can not be considered as exerting tlie 

 slightest evil influence, and its physiological effects are practically nil. 

 The increase of pressure is much more important in the case of diving 

 bells, and it is among workmen who are engaged in the building of 

 piers and wharves, or in the exploration of wrecks, that we must search 

 for information concerning the effects of high atmospheric pressure, 

 unless we turn to animals exi)erimentally subjected to such condition 

 in bell jars connected with forcing pumps. When the increase is 

 slight, the effects are also slight. Some buzzing in the ears, some 

 bleeding at the nose, and a slight numbness in the limbs are those 

 which are most api)reciable. But, at the same time, the respiration 

 and circulation are slower. In some cases there occurs an abnormal ex- 

 citation of the nervous system similar to that observed during acute 

 alcoholism. Such accidents are quite naturally ascribed to an increase 

 in the tension of carbonic acid, which accumulates in the system and 

 determines incipient asphyxia. This interpretation is correct as long 

 as the increase of pressure is moderate. But when the increase of 

 pressure is considerable, when we have to deal with pressure of six or 

 more atmospheres, the case is altered, and the cause of the symptoms 

 is different. This is shown by Paul Bert's various experiments. In 

 order to delay the effects of increase of pressure, he added pure oxygen 

 to the atmosphere inspired by tlie animals experimented upon, expect- 

 ing by this means to prevent the toxic influence of carbonic acid. He 

 was, therefore, considerably surprised when he perceived that this 

 had no other result than to hasten the fatal issue. He then proceeded 

 to a careful analysis of the symptoms and phenomena, and perceived 

 that when the pressure is over 6 atmospheres the oxygen contained 

 in the atmosphere, acquiring a high tension, becomes a poison. And 

 none can wonder at this. An increase of the proportion of oxygen 

 under normal pressure is attended by toxic symptoms; an increase 

 in the pressure of oxygen, which amounts to the sauje thing, must 

 exert the same influence. And the i)roof that oxygen is the only cul- 

 prit lies in the fact that an animal can perfectly well endure a pres- 

 sure of 20 atmosi^heres if the air is i^oor in oxygen, if oxygen, 

 being less in quantity, has, in the mixture, a tension which does not 

 exceed that which the normal amount of oxygen, in normal air, pos- 

 sesses under normal pressure. Under increased tension, as well as in 

 increased proportion — for both conditions are identical as far as physi- 

 ology is concerned — oxygen is a poison, and a very dangerous one, and 

 this is the reason why man and animals die in a normal atmosphere, 

 when the pressure exceeds certain limits. Be it rapid or slow, consid- 

 erable increase of pressure kills through the agency of oxygen and of 

 its toxic properties, by reason of oxygen being dissolved in the blood 

 serum. If we leave out of consideration those cases where the varia- 

 tions of pressure are rapid, and where, as is the case with rapid decrease 



