GIL XXVII.] CARBON MONOXIDE POISONING 403 



not possible, therefore, for men to work in air which is compressed 

 to the extent of producing so great a pressure of oxygen. 



Caisson disease. In the boring of tunnels and in carrying out 

 operations in the beds of rivers, it is usual to sink an iron tube in 

 which the men work. This tube or caisson is closed except at the 

 end at which the work is progressing, and the water is prevented 

 from inundating it by pumping air into it at a pressure higher 

 than that of the water. The men enter through a chamber with 

 double doors or "air-lock." In this chamber the pressure can be 

 raised or lowered. The pressure in the caisson rarely exceeds 

 4 atmospheres, which corresponds to about 600 mm. of oxygen; 

 at this pressure the workers do not suffer whilst they are in the 

 caisson, but grave symptoms may take place shortly after they have 

 come out. Similar symptoms are experienced by divers who come to 

 the surface from great depths. The symptoms may take the form of 

 paralysis, vomiting, severe abdominal pain, vertigo, etc. They are due 

 to the fact that the plasma, and indeed all the fluids which permeate 

 the organs of the body, become saturated with oxygen and nitrogen 

 at the pressure of the caisson, and therefore when the pressure 

 is suddenly removed, minute bubbles form throughout the body 

 and injure such tissues as the spinal cord, or produce blockage 

 of the vessels. Short hours are necessary for caisson workers, for 

 then the body has not time to get saturated with air at the caisson 

 pressure, and in all cases "decompression" must be gradual and 

 slow; this gradual release from pressure is accomplished in the 

 " air-lock." The dangers we have mentioned then cease to exist. 



The atmospheric gases are specially soluble in fat; fat people 

 are therefore very susceptible to caisson disease, and should, in fact, 

 be prohibited from labour in caissons. 



Carbon Monoxide Poisoning. 



The fatal effects often produced by this gas (as in accidents from 

 burning charcoal stoves in small close rooms, or where there is an 

 escape of coal gas), are due to its entering into combination with the 

 haemoglobin of the blood-corpuscles, and thus hindering their oxygen- 

 carrying function. In an atmosphere containing both oxygen and 

 carbon monoxide, the relative quantities of the two gases which the 

 haemoglobin will absorb varies with the partial pressure of the 

 gases. The affinity of haemoglobin for carbon monoxide is, how- 

 ever, much greater than its affinity for oxygen, and the compound 

 formed carboxyhaemoglobin is much more stable than oxy haemo- 

 globin is. If, therefore, any considerable quantity of carbon mon- 

 oxide is present in the air, the haemoglobin will be almost completely 

 charged with carboxyhaemoglobin, and asphyxia would follow. If 

 the patient is given pure oxygen to breathe even at a late stage, 



