RESPIRATION 299 



when the pressure of the oxygen is far less than usual. 

 Nevertheless a sufficiently radical reduction of the 

 oxygen pressure tends to lessen the amount received by 

 the blood and the want begins to be felt in the nervous 

 system. Deficiency of oxygen supply to active tissues 

 has one outstanding result: it leads to an accumulation 

 of acid, to acidosis as we say. 



The acid which begins to gather when the oxygen 

 supply is short is chiefly lactic. We have already men- 

 tioned this among the fatigue substances arising in work- 

 ing muscle. It can be rapidly and completely removed 

 if oxygen is freely obtainable. If its formation con- 

 tinues it acts as a poison. Mountain sickness, the 

 combination of ill effects experienced by those who 

 go to high altitudes for the first time, is believed to be 

 due mostly to lactic acid formation. As observed on 

 Pike's Peak in subjects who are not exerting them- 

 selves it is said to begin with a period of nervous irrita- 

 bility. This is succeeded by nausea and vertigo and 

 these symptoms in their turn by persistent and severe 

 headache. The sequence is like that exhibited in 

 connection with alcoholic indulgence. 



While these manifestations are best explained as signs 

 of acidosis it has been suggested by writers dealing with 

 this subject that a certain degree of acapnia is to be 

 expected. In a rarefied atmosphere the breathing must 

 be deepened to keep an adequate oxygen pressure in the 

 alveolar air. There is no difficulty, however, in working 

 off the carbon dioxid which leaves the blood quite as 

 freely as at the sea-level. An awkward dilemma arises: 

 the breathing must be forced to secure enough oxygen, 

 yet it cannot be forced without establishing some 

 measure of acapnia. 



Acclimatization. It would be interesting to know all 

 the changes which take place in the human system when 

 it is becoming adapted to life at an altitude previously 

 unwonted. One of the earliest to be recognized was 

 a marked increase in the number of the red corpuscles. 



