Decreased Pressure 983 



sphygmographic graphs of M. Lortet, taken just as he arrived at 

 the summit of Mont Blanc, it is hard to find indication of the pulse. 



And so the organism, conquered in its struggle to compensate 

 for the diminished density of the oxygen in the air by agitation 

 of the air and the blood, returns to the regular routine of its move- 

 ments, which the poverty of the blood soon weakens. At this time, 

 the seriousness of the phenomena begins to increase rapidly; the 

 blood's insufficient capacity for oxygen is complicated by a greater 

 and greater imperfection in the intra-pulmonary ventilation and 

 circulation caused by the insufficiency of the oxygen absorbed. 

 That is why, as we have seen, the arterial blood of animals under 

 decompression contains even less oxygen than it might absorb at 

 that given pressure. 



This rapid decrease in the oxygen content of the blood causes a 

 profound disturbance in metabolism and consequently in the func- 

 tioning of the organs. We have seen that in animals placed under 

 bells with rarefied air, when the decompression is great enough, 

 the quantity of carbonic acid exhaled and of urea excreted dimin- 

 ishes considerably; the temperature drops also, even when that of 

 the outer air is average. The same thing must certainly happen to 

 aeronauts, when they reach very great heights, where, in addition, 

 the air is generally very cold. I recall that I showed experimentally 

 that in cold air, resistance to decompression is less than at ordi- 

 nary temperatures. 



But under decompressions lower than those which we had to 

 use to show experimentally, that is, roughly, the diminution of the 

 inner workings of metabolism, it is revealed to the observer by the 

 functioning of the organs. But here, as is always the case when 

 we have to do with a cause capable of affecting the whole or- 

 ganism, it is. the nervous system which reacts first, which is the 

 first to complain, if I may use this expression. The sensation of 

 fatigue, the weakening of the sense perceptions, the cerebral symp- 

 toms, vertigo, sleepiness, hallucinations, buzzing in the ears, dizzi- 

 ness, pricklings, reactions of the pneumogastric and sympathetic 

 nerves, nausea, palpitation, dilation of the arterioles are the signs 

 of insufficient oxygenation of central and peripheral nervous or- 

 gans. After the nervous system comes the muscular system, which 

 betrays weakness, is seized by convulsive contractions, and by 

 shudders, in which the nervous system also certainly has its part. 

 Finally, in the last stages, come paralysis, syncope, or to speak more 

 exactly, loss of consciousness, and finally death without a last sigh 



