76 APPLIED PHYSIOLOGY 



this increase, attempts to arrive at an explanation of 

 which have led to much controversy, cannot be discussed 

 here,* but it may be said in brief that, whilst in part the 

 increase is apparent only, and due to an altered distribu- 

 tion of the blood which is driven out of the abdominal 

 organs by the deeper respiration which life at high 

 altitudes entails, and also, perhaps, to a concentration 

 of it from increased cutaneous evaporation, yet most 

 observers admit that in part the increase is real and 

 due to a greater formation of red cells. The natural 

 teleological explanation of such increased formation is, 

 of course, that it is an attempt to compensate for the 

 greater difficulty of oxygenating the blood experienced 

 at high elevations, more corpuscles being exposed to the 

 air to make up for less oxygen being taken up by each 

 individually. At all events, whatever the real explana- 

 tion is, many of the valuable therapeutic effects of 

 residence at high altitudes have been attributed to this 

 increased formation of blood. Unfortunately, however, 

 the number is soon reduced on return to lower levels. 



A pathological increase in the number of red cells is 

 not common, and may be apparent only the result of 

 stagnation of blood in the capillaries and its consequent 

 inspissation. On the other hand, all cases are not to be 

 so explained, and in the form of polycythaemia associated 

 with splenic enlargement the evidence points rather to 

 an increased formation of red cells. It is interesting to 

 note that there would seem to be a limit to the extent 



* For a full discussion of the subject, see Pacht, * Ueber die 

 Veranderungen des Blutes im Hochgebirge,' St. Petersburg 

 Med. Woch., 1901, xxvi, 543. 



