394 PHYSIOLOGY. 



that the color of the blood after death from asphyxia from carbon 

 monoxide is cherry-red; in other forms of asphyxia the blood is 

 almost black. These occur from poisoning by coal-gas (especially 

 where charcoal stoves are used in small rooms), the fumes of kilns and 

 coke-fires, and from inhaling the air of coal-mines, especially after 

 explosions. 



Caissons and the Effect of Compressed Air. In caissons men are 

 able to support during some moments a pressure of five to ten atmos- 

 pheres when they proceed with caution. If the pressure is too rapid, 

 there is great danger. On decompression pains in the joints and 

 muscles ensue, followed by paralysis, with deafness and vertigo. 

 These symptoms are called "bends." 



When an animal that resists a pressure of ten atmospheres dies 

 instantly from a rapid change to ordinary pressure, the autopsy 

 shows that the heart and large vessels are filled with bubbles of gas, 

 especially of nitrogen. Under the influence of double or triple pres- 

 sure the blood absorbs a double or triple proportion of air, especially 

 the nitrogen. If the animal is submitted to a rapid diminution of 

 pressure, the nitrogen, not being kept in solution in the blood, is 

 disengaged in a gaseous state in the form of bubbles, which produce 

 embolism in the capillaries of the brain, lungs, and heart, and arrest 

 the circulation. To avoid the disengagement of bubbles of nitrogen 

 it is necessary to let the atmospheric compression down in a very 

 gradual manner. Operatives on leaving the tubes in which com- 

 pressed air exists must remain a quarter to a half hour in the closed 

 chambers, where the pressure is reduced little by little. The excess 

 of gas absorbed is slowly eliminated by the lungs without producing 

 an accident. Four atmospheres is about the amount that operatives 

 can work in with safety. Every ten meters of depth in water roughly 

 equals one atmosphere. By itself compressed oxygen is a toxic 

 agent, for it lowers the output of carbonic acid and the temperature 

 of the body. The cure for caisson-paralysis is recompression and 

 slow decompression. 



Hill and McLeod have shown that in compression air chambers 

 there was no alteration of blood-pressure or pulse-rate, or in the 

 diameter of the blood-vessels, or in the rate of the flow of blood. A 

 rise of atmospheric pressure exercises no mechanical effect upon the 

 circulation. Hill and McLeod have shown that the oxygen of the 

 air compressed produces inflammation of the lungs, just like ether 

 or any other irritant. This inflammation is produced in an hour or 

 two with high pressures. 



