1906.] on Compressed Air and its Physiological Effects. 375 



+ '!-?> atm. I should be sorry to be decouipressed at any rate quicker 

 than 20 minutes per atm. The lock should be made a comfortable 

 room, warmed and hghted. The men (durino- decompression) should 

 carry out muscular movements of all parts of the body, so as to hasten 

 the circulation and carry the Ijlood quickly through the lungs. 



A band of men trained in patience to l)e so decompressed, might 

 carry out tunnelling operations at a depth hitherto not dared l)y the 

 engineer. For deep-sea divers I have designed a bell which the diver 

 can enter at the bottom of the sea, and in which he can be slowly and 

 safely decompressed after the bell has been raised on deck. With such 

 an apparatus, I believe it will be possible to salvag:e wrecks at depths 

 of 200 ft. 



I now turn to the consideration of the influence of high pressures 

 of oxygen on life. Contrary to preconceived opinion, we find the 

 rate of combustion of an animal cannot be accelerated, as that of a 

 fire can be, by increasing the supply of oxygen. The living tissues 

 set their own rate of metal)oHsm, and neither the inhalation of oxygen 

 nor exposure to compressed air can be used as a therapeutic agent to 

 increase the normal rate of tissue change. It is only cases where the 

 oxygen supply is deficient — such as severe anaemia, carbon monoxide 

 poisoning, congenital disease of the heart, pneumonia, etc. — where the 

 tissues, and in particular the heart itself, are suffering from oxygen 

 hunger ; it is only these cases that can be benefited by oxygen in- 

 halations. 



It is a remarkable thing that the continued action of oxygen at a 

 pressure of 1 atm. and over acts as a poison (Bert, Lorrain Smith, 

 L. Hill and Macleod). It produces inflammation of the lungs, 

 depresses the respiratory exchange, and lowers the body temperature ; 

 at pressure of 2-6 atm. it quickly produces general epileptiform con- 

 vulsions, and these are followed by a gasping type of breathing, coma, 

 and death. All terrestrial animals, as far as I have tried them, are 

 instantly thrown into convulsions and killed by exposure to 50-60 atm. 

 of oxygen. 



On the other hand, the excised hearts, muscles, and nerves of 

 frogs. I find, survive the exposure to such a pressure for an hour, 

 although with somewhat abated vigour. Tlie swim-bladder of the 

 fish must be immune to oxygen poisoning, for in a fish, caught at a 

 depth of 4500 ft., whose bladder contained almost pure oxygen, the 

 tension at which this gas was secreted was nearly 135 atm. ! 



The lungs and the nerve cells seem to be the especial points of 

 attack by high pressures of oxygen. It requires, I find, an exposure 

 for about 24 hours at 8 atm. of air (the oxygen pressure = 167 per 

 cent, of an atm.) to produce marked pulmonary congestion ; no such 

 result follows if the oxygen in the air be halved by the addition of 

 N2. Owing to the danger of oxygen poisoning it will not be advis- 

 able for men to work for long periods at high pressures. Oxygen 

 at a tension of 180 per cent, of an atm. kills mice in 24 hotirs, while 



