344 RESPIRATION 



rendered possible for divers to work at great depths without in- 

 convenience. The existing precautions against "caisson disease" 

 were evidently quite insufficient. The divers were officially en- 

 joined to descend and come up at a slow and even rate of about 

 5 feet per minute, but many serious or fatal cases were occurring 

 in spite of this. The problem was to find a safe and reasonably 

 short method. Very slow methods are impractible on account of 

 changes of tides and weather. The whole physiological side of 

 compressed-air illness had therefore to be reconsidered. 



The formation of bubbles depends, evidently, on the existence 

 of a state of supersaturation of the body fluids with nitrogen. 

 Nevertheless there was abundant evidence that when the excess 

 of atmospheric pressure does not exceed about i% atmospheres 

 there is complete immunity from symptoms due to bubbles, how- 

 ever long the exposure to the compressed air may have been, and 

 however rapid the decompression. Thus bubbles of nitrogen are 

 not liberated within the body unless the supersaturation corre- 

 sponds to more than a decompression from a total pressure of 

 2/4 atmospheres. Now the volume of nitrogen which would 

 tend to be liberated is the same when the total pressure is halved, 

 whether that pressure be high or low. Hence it seemed to me 

 probable that it would be just as safe to diminish the pressure 

 rapidly from 4 atmospheres to 2, or 6 atmospheres to 3, as from 

 2 atmospheres to i. If this were the case, a system of stage 

 decompression would be possible, and would enable the diver to 

 get rid of the excess of nitrogen through his lungs far more 

 rapidly than if he came up at an even rate. The duration of ex- 

 posure to a high pressure could also be shortened very consid- 

 erably, without shortening the period available for work on the 

 bottom. 



The whole matter was put to the test in a long series of experi- 

 ments carried out on goats by Professor Boycott, Commander 

 Damant, and myself 6 at the Lister Institute, London, in a large 

 steel chamber which was given for the purpose by the late Dr. 

 Ludwig Mond (see Figures 86 and 87). We found that after 

 very long exposure of a number of the animals at a total pressure 

 of 6 atmospheres sudden decompression to 2.6 atmospheres pro- 

 duced not the slightest ill effect. This decompression is in the 

 proportion of 2.3 to I, and the drop of pressure was 3.4 atmos- 

 pheres. In a corresponding series where the drop of pressure was 



a Boycott, Damant, and Haldane, Journ. of Hygiene, VIII, p. 242, 1908. The 

 Report of the Admiralty Committee contains a short abstract of the work. 



