278 Chapter XVIII 



And now to turn to the physiological significance of the meionexy 

 and of the acidosis. 



The essence of any mechanism of adaptation to high altitudes 

 must be a " speeding up " of the whole process of respiration, physical 

 and chemical. The blood in the lung is exposed to a lower oxygen 

 pressure than usual ; it is saturated to a less extent with oxygen 

 than formerly. The tissues begin to suffer from oxygen want : a very 

 trifling change in the blood is enough to produce a great change in 

 the circulatory conditions ; the pulse quickens, respiration becomes 

 deeper and more rapid, the amount of blood which leaves the lung 

 increases perhaps twofold. Let the reader picture to himself each 

 corpuscle as a ship with its little cargo of oxygen and twice as many 

 of these are leaving the lung as before ; they go to the tissue and go 

 through the capillary at perhaps twice their former velocity ; but stay 

 how are they to unload their cargo in the reduced time at their 

 disposal? How futile would be the whole scheme if the corpuscle bolted 

 through the capillary carrying its oxygen into the vein with it. Here 

 is the advantage of meionexy. The meionectic blood parts with its 

 oxygen with much greater rapidity than does the normal blood under 

 given circumstances. Therefore when the corpuscle gets to the capil- 

 lary it can discharge its cargo with unusual facility. 



It is true that the meionectic blood is at a disadvantage in the 

 lung. It probably has not time in the lung to become saturated to 

 quite the degree that normal blood would. But blood saturates 

 itself up to 80 or 85 % very rapidly, and the organism must take the 

 risk of doing without the rest, it meets the small deficiency in the 

 degree of oxidation by a large increase in the quantity of blood 

 leaving the lung. The thing of course is a compromise, you must 

 lose something somewhere. You cannot pretend that the organism 

 is not working at a disadvantage at an altitude of 15,000 feet. It is 

 making the best of a bad business. The best it can make is meionexy. 

 Meionexy involves stimulation of the neuro-muscular mechanism of 

 respiration and quickening of the proportionate rate at which the 

 blood loses oxygen in the tissues. 



But at slow rates of climbing the degree of acidosis is much 

 greater than the degree of meionexy. Including the carbonic acid 

 the blood becomes to a small extent more acid than formerly, but 

 the blood becomes much richer in other acids and poorer in C0 2 than 

 before. The carbonic acid is displaced in the blood and after a pre- 

 liminary rise it ultimately decreases in the alveolar air. Therefore the 



