368 Mr. Leonard Hill [May 25, 



time the whole body becomes satm-ated, according to Dalton's law. 

 From his analyses Bert concluded that the absorption of N2 la.gged 

 behind the requirements of Dalton's law. This was due to his taking 

 too high a figure for the coefficient of absorption of X2 in l)lood. 

 The saturation of the body fluids must take time, since the blood 

 forms but 5 per cent, of the whole body weight (Haldane), and it is 

 the blood alone that comes in direct contact in the lungs with the 

 increased atmospheric pressure. Probably about 5 litres of Ijlood 

 circulate through the lungs per minute, and this blood conveys the 

 absorbed nitrogen to the 30-40 litres of water which are in the body. 

 The arterial blood saturated in the lungs yields the nitrogen to the 

 tissues, and returns to be saturated again in the lungs. Those 

 tissues, which are plentifully supplied with blood, will become 

 saturated rapidly, while less vascular areas, and parts in a state of 

 vaso-constriction, will saturate very slowly. 



C. Ham and I exposed rats to 10-20 atm., killed them by instant de- 

 compression, and then mincing their bodies under water, collected and 

 analysed the gas set free therein. We obtained in this gas CO^ 6 * 7 

 — 16 per cent., O2 2-1 — 8*7 per cent., N2 80 — 87 per cent., and a 

 volume of N2 even greater than that calculated by Dalton's law. 

 The excess we found was due to gas swallowed while under pressure. 

 Most of the gas, set free on decompression from such high pressures, 

 is free in the peritoneal cavity and alimentary canal. 



M. Greenwood and I have tested upon ourselves the rate of satu- 

 ration, using the urine as a test fluid. We were compressed in a 

 large boiler, placed at our disposal by Messrs. Siebe, Gorman and Co. 

 The chamber was fitted with electric light and telephone, and taps 

 for slow decompression. The pressure was raised by means of a 

 diving pump driven by a gas engine. We drank a quart of water 

 before entering, and collected samples of urine at varying pressures 

 and times. The urine, collected in sealed bulbs, was evacuated by 

 my blood gas pump. We found the urine secreted in the next 10 

 minutes after reaching any given pressure is saturated with N'o at 

 that pressure. Oxygen as well as nitrogen is dissolved, but this is of no 

 importance, because the oxygen chemically combines with the blood 

 and tissues on decompression. 



To demonstrate the bubbling off of nitrogen on rapid decom- 

 pression, I have spread the web of frog's foot or wing of bat over 

 the glass window of a pressure chamber. The circulation of the 

 blood is projected on a screen with aid of microscope and arc light. 

 AVe can thus observe the circulation under 20 atm. of air, and watch 

 the bubbles forming in the capillaries on rapid decompression. The 

 com])ression diminishes the size and finally drives the bubbles again 

 into solution. 



When the larger mammals are exposed to high pressures, such as 

 8 atm., for an hour or so, and are then rapidly decompressed, they 

 usually die in a few minutes. Small mammals, such as mice and rats, 



