THE EFFECTS OF EXCESS OF CARBON DIOXIDE 311 



"by swallowing, or by an expiratory effort made with the mouth and 

 nose shut. 



The symptoms of sickness range from small pains in the joints 

 and muscles, known as " bends," to sudden paralyses or death. The 

 subject has been thoroughly studied experimentally (Figs. 173, 174) and 

 the cause of the trouble is now clearly understood. At high pressures 

 the blood and fat take up large quantities of nitrogen in simple physical 

 so!ution. When the pressure is reduced rapidly, the nitrogen becomes 

 freed in the circulation, and, becoming lodged as bubbles of gas in 

 various parts of the body, produces symptoms of varying severity 

 according to the degree of damage and the site of injury (see 

 Figs. 175-178). Rapid decompression is therefore the danger. The rate 

 of decompression must be regulated according to the pressure and period 

 of saturation of the body. A diver who has been for a short time at 



PIG. 178. NECROTIC AREAS (PALE) IN POSTERIOR COLUMNS OF SPINAL CORD, FROM 

 A FATAL CASE OF COMPRESSED AIR ILLNESS, (v. Schrotter.) 



a great depth may be relatively more quickly decompressed than a 

 man who has been working several hours in a less pressure. The 

 decompression is carried out in stages, for it is safe to allow a certain 

 amount of supersaturation, as bubbles do not easily form in the blood 

 e.g., the diver ascends rapidly from a depth of 100 feet (4 atmos- 

 pheres) to 33 feet (2 atmospheres), and pauses there for some time, 

 meanwhile exercising his muscles to accelerate the circulation and 

 ventilation of the lungs, and so wash the excess of dissolved nitrogen 

 out of his body. He then returns to the surface. For each atmos- 

 phere of air the water of the body dissolves about 0-8 per cent, of 

 nitrogen. As fat dissolves five to six times as much nitrogen as 

 water, there is particular danger of bubbles forming in the nervous 

 tissues. All fat men are excluded from work in deep water. 



The solution of nitrogen in the body fluids during compress: on 

 and the giving out of the excess of dissolved nitrogen during decom- 

 pression has been studied on subjects who drank a quart or so of water 

 just before entering the chamber, and collected samples of their mine 

 at various stages of compression and decompression. The nitrogen 

 dissolved in these samples was pumped out by means of the mercury 

 gas pump and estimated. 



