TRANSACTIONS OF SECTION I. 757 



five hundred manshifts were decompressed from +40 lb. in 48 minutes, with 

 1'62 per cent, cases and no seriojs ones. The method was (1) +40 to +29 lb. in 

 five minutes; (2) ten minutes' walking in +29 lb.; (3) +29 to +125 lb. in 

 eight minutes; (4) ten minutes' walking in +12'5 lb.; (5) +12 5 to +0 in fifteen 

 minutes. The Admiralty table ordains 92 minutes for this pressure. About 

 half this time evidently is enough. 



' Slow ' parts produce bends which do not matter : they can be relieved by 

 recompression. 



Statistics of the results of ' uniform stage ' decompression obtained on goats by 

 Boycott, Damant, and Haldane ; on guinea-pigs by Boycott and Damant ; on 

 rabbits, pigs, and goats by the writer and Greenwood, taken together, afford no 

 convincing evidence of the superiority of either method. The pig is a better 

 animal to compare with man than a goat. The fermentation of gas in the goat's 

 stomach complicates the problem. Comparable pig figures show 4 severe or fatal 

 cases in 20 uniform, 9 in 32 stage, 9 in 44 modified uniform (decompression rate 

 slowing as pressure falls). The time of decompression was 90 to 110 minutes, 

 the pressure +75 lb. Decompression in 37 to 45 minutes killed 4 out of 4 by 

 stage; 4 out of 8 (and 3 severe cases) by uniform. These were small pigs, 

 weighing 33g lb. to 49 lb. F. J. Twort and the writer have determined the 

 desaturation of water when decompressed from +90 to +20 lb. in 10 minutes; 

 and either (1) left quiet, (2) shaken, (3) gently oscillated, the gas comes off 

 without bubbling in 1 and 3. In the case of oil there is a slow steady formation 

 of small bubbles (O'l to 03 mm. in diameter). The unstudied conditions which 

 control bubble formation in supersaturated solutions are of the first importance. 

 ' Delayed ' illness and varying susceptibility depend on these influences. 

 The varying percentage of fat in blood, chyle, liver, and the gaseous contents 

 of the guts are factors. Ill-health, a debauch, rich feeding modify these condi- 

 tions. (Fat, 3 to 11 per cent, in chyle, in liver 2 to 3'5 per cent, in richly fed, 

 19 to 24 per cent, in fatty infiltration.) 



Experiments by M. Greenwood and the writer show that it is fairly safe to 

 decompress pigs and goats from +75 to +18 lb. in 10 minutes, and from 

 + 18 to +0 in 20 minutes, after an interval of 80 to 100 minutes. 



One death and no severe case resulted in 47 pigs weighing 50 to 100 lb. ; 

 1 severe, 3 slight cases in 19 goats weighing 39 to 57 lb. To these may be added 

 4 pigs (56 to 100 lb.) safely decompressed from +60 lb. Decompression from 

 +90 to +20 lb., followed by an interval of 105 to 120 minutes, gave unfavourable 

 results in fat pigs weighing 81 to 115 lb. — viz., 7 deaths and 1 severe case in 

 27 pigs. The deaths occurred in the pigs which had the shortest interval, 105 to 

 110 minutes. Two of these deaths and the severe case were due to the pump 

 stopping at +20 and the chamber rapidly leaking out. 



Only one pig out of all showed symptoms at +20 lb. The pigs lie asleep and 

 do not move. Six goats compressed after a big feed were all taken with 

 great gaseous distension of the stomach at +20 lb. 



By extending the interval to 140 to 150 minutes three goats (on a spare diet) 

 were decompressed successfully time after time after exposure to +90 lb. for 

 three to four hours. An interval of 30 to 50 minutes at +15 lb. proved safe for 

 12 goats and 1 pig (96 lb.), after compression to +50 lb. 



Experiments by H. B. Walker, F. J. Twort, and the writer show that the 

 breathing of oxygen for a few minutes at +15 lb. washes the excess of nitrogen 

 out of the urine (and blood) quickly, while only a little oxygen passes into the 

 urine. It is safe to breathe oxygen for some minutes at +15 lb., but inadvisable 

 to breathe it at higher pressures because of the toxic effects of high pressures of 

 oxygen. 



Experiments of M. Greenwood and the writer show that a partial pressure of 

 C0 2 up to 1 to 2 per cent. atm. is of no importance. Hot, moist atmospheres are 

 exhausting. Many of the pig experiments were conducted with 4 to 5 per cent, 

 atm. C0 2 in the chamber, and this was unfavourable, as the partial pressure fell 

 on decompression, and lessened the pulmonary ventilation. Ventilation should be 

 reduced in the lock. The cooling effect of decompression should be prevented, 

 for it constricts the cutaneous vessels. 



M. Greenwood and the writer were safely decompressed from +75 lb. by 

 the uniform method — about 20 minutes per atm., four experiments. They were 



