128 RESPIRATION 



The best-known delayed effect of slight anoxaemia is the train 

 of symptoms originally called "mountain sickness." This is a 

 condition in the typical form of which there is nausea, vomiting, 

 headache, sometimes diarrhoea, and always great depression. The 

 symptoms appear, as a rule, some hours after the beginning of 

 the exposure, and may not appear at all till after the exposure is 

 over. In CO poisoning it is usually after the exposure, and often 

 after the CO has practically disappeared from the blood, that 

 these symptoms begin. The duration of exposure required for their 

 production depends upon the degree of anoxaemia. Thus the 

 higher a mountain is, or the greater the altitude at which an air- 

 man has been flying, the shorter is the exposure required. On 

 Pike's Peak, at 14,100 feet (barometer about 458 mm.) the usual 

 stay (an hour or two) of visitors by train is too short to produce 

 mountain sickness, though the ordinary immediate symptoms of 

 anoxaemia are usually very evident, and even very great cyanosis 

 and fainting are observed occasionally. A stay of several hours 

 is usually required to induce mountain sickness, which usually 

 begins about 8 to 12 hours after the beginning of the exposure. 

 Thus the symptoms may only develop after the return downwards. 



With a sufficient period of exposure mountain sickness may 

 develop at much lower altitudes than that of Pike's Peak. It is 

 often observed at even 7,000 or 8,000 feet, where the degree of 

 anoxaemia is not sufficient to produce any noticeable immediate 

 effect on the breathing. Similarly a percentage of CO which pro- 

 duces no noticeable immediate effect will, with sufficiently long 

 exposure, cause headache, nausea, etc. These facts are of the 

 greatest significance in clinical medicine, for it is now evident that 

 even a very slight degree of continued anoxaemia is of much 

 importance to the patient. Mountain sickness and the effects of 

 CO poisoning are not isolated phenomena unrelated to the rest of 

 physiology and pathology, but symptoms of anoxaemia, which is 

 in reality one of the commonest conditions during illness. At 

 present we can only conjecture as to the nature of the slight 

 temporary pathological changes of which the mountain sickness 

 symptoms are the manifestations. 



With severe and prolonged exposure to want of oxygen the 

 nervous after symptoms are of an extremely formidable nature, 

 and often end in death. ^^ For a reason which will be explained 



" An interesting description of these symptoms by Dr. Shaw Little will be 

 found in Appendix B to my Report on the Causes of Death in Colliery Explosions 

 Parliamentary Paper C. 8112, 1896. 



