240 RESPIRATION 



the lactic acid present in the urine during moderate work. Thus the 

 anoxaemia cannot well be due to anything else but imperfect 

 saturation of the arterial blood with oxygen; and that this is the 

 actual cause is directly shown by the fact that a very moderate 

 increase in the oxygen percentage of the air breathed relieves the 

 symptoms. 



In ordinary persons not in good physical training a very mod- 

 erate diminution in atmospheric pressure is quite sufficient to 

 cause a noticeable excess of hyperpnoea on any considerable ex- 

 ertion, such as climbing or walking fast. This is very evident on 

 going by train to some place four or five thousand feet above sea 

 level; and the cause is, without a shadow of doubt, imperfect 

 oxygenation of the arterial blood. At ordinary atmospheric pres- 

 sure we are accustomed to a certain degree of hyperpnoea and 

 exhaustion with a given degree of muscular exertion. That this 

 is in part dependent on imperfect saturation of the arterial blood 

 is only revealed by the fact that in air at a higher atmospheric 

 pressure (as in the case of workers in compressed air, and prob- 

 ably in deep mines), or when air enriched with oxygen is 

 breathed, the same work becomes much easier, at any rate to many 

 persons. 



The observations of Dr. Henry Briggs, described in Chapter 

 VII, show that there is a striking difference in this respect be- 

 tween men in good physical training and ordinary persons, as the 

 former class get no benefit from air enriched with oxygen unless 

 the work is excessively hard, while the latter get great benefit, 

 shown, not only by the much greater ease and comfort with which 

 they perform the work, but by the smaller amount of air which 

 they require to breathe. The corresponding difference at high 

 altitudes is perfectly familiar to mountaineers. The man who is in 

 good training is free from the hyperpnoea, mountain sickness, and 

 other effects of high altitudes to a far greater extent than the man 

 who is not in training; and this evident fact has often led 

 mountaineers to the mistaken conclusion that mountain sickness 

 has nothing to do with altitude or anoxaemia, but is simply a sign 

 of imperfect training. 



All the facts just mentioned confirm the direct evidence in 

 favor of oxygen secretion in the lungs. Part of the exhaustion of 

 hard physical work is due to imperfect saturation of the arterial 

 blood with oxygen and the consequent effects on the respiratory 

 center and central nervous system as already described in Chap- 

 ters VI and VII. In persons who are in good physical training 



