RESPIRATION 351 



and no compressed-air chamber is available, the best plan is to 

 screw on his helmet and drop him down under water till his 

 symptoms disappear. An unconscious man (who had developed 

 bad symptoms as a result of disregarding orders to stop at the 

 proper stages) soon answered the telephone when he was dropped 

 down in this way. The trouble, however, is to get the man up 

 again safely. A very cautious ascent is needed. When once bubbles 

 of any considerable size have formed it takes a considerable time 

 to get them redissolved. 



The reason why a bubble in the blood or elsewhere in the body 

 tends to disappear, is that the partial pressure of nitrogen in the 

 bubble is greater than in the blood. The blood is saturated in the 

 lungs with nitrogen at a pressure of about 75 per cent of the 

 existing atmospheric pressure. In the venous blood, and there- 

 fore in the tissues, the pressure of oxygen, as shown in Chapter X, 

 is only about 6 per cent and of CO 2 about 6.5 per cent of an 

 atmosphere. There is also a pressure of about 6 per cent of aqueous 

 vapor. As the bubble is at atmospheric pressure and the total gas 

 pressure in the surrounding tissues is only about 75 -}- 18.5 = 

 93.5 per cent of an atmosphere, its nitrogen pressure is above that 

 of the tissues by 6.5 per cent. It must therefore gradually go into 

 solution, and at high atmospheric pressures it will do so all the 

 sooner since the pressures of oxygen and CO 2 do not increase pro- 

 portionally to the atmospheric pressure. If the bubbles are only 

 very small they will probably dissolve very rapidly on recompres- 

 sion; but if they are large, and particularly if they have been 

 formed at places where there is but little circulation, they will take 

 a long time to disappear. Great patience may therefore be needed 

 in treatment by recompression. 



In the experiments made at sea under the direction of the 

 Admiralty Committee, the greatest depth at which trials were 

 made was 35 fathoms. At this depth Commander Damant and 

 Lieutenant Catto were perfectly comfortable, and in all the 

 numerous experimental dives which they made up to this depth 

 with stage decompression, no symptoms whatever of compressed- 

 air illness were observed. This depth was, however, greatly ex- 

 ceeded in the course of operations for the recovery of a United 

 States submarine at Honolulu in 1915. A diving crew had been 

 trained in the new methods at New York, and proceeded to Hono- 

 lulu to assist in getting hawsers in position round the submarine, 

 which was lying at a depth of 50 fathoms (corresponding to an 

 excess pressure of over 9 atmospheres or 135 pounds per square 



