RESPIRATION 



293 



bleeding the reproduction of the red corpuscles becomes more and 

 more rapid, so that finally the animal can reproduce the lost cor- 

 puscles very rapidly. Similarly on repeated transfusion the animal 

 can get rid of the transfused corpuscles more and more rapidly. 

 It thus becomes adapted to either bleeding or transfusion. 



In an animal in which as a result of bleeding or similar causes 

 the proportion of haemoglobin in the blood is abnormally low the 

 oxygen pressure must fall more rapidly than usual if the rate of 

 circulation is unaltered, as the blood passes through the tissues. 

 In accordance with what has been already said, this will naturally 

 tend to be more or less compensated for by an increased rate of 

 circulation. But this can occur freely without the opposing effect 

 due to the production of alkalosis, since owing to the diminished 

 percentage of haemoglobin the pressure of CO2 would also be 



Figure 72. 

 Ordinates represent percentages of the average haemoglobin percentages 

 obtained before ascending the Peak (Oxford and Colorado Springs) on the 

 particular subject. Continuous thick line = total oxygen capacity or total 

 amount of haemoglobin. Continuous thin line = percentage of haemoglobin. 

 Interrupted line = blood volume. The values in Oxford before the start of 

 the expedition are plotted without relation to time. 



too high unless the circulation rate were increased. An increased 

 circulation rate is thus the natural response to a diminished haemo- 

 globin percentage. 



We know from observations on persons living at high altitude 

 that one result of the shortage of oxygen caused by the diminished 

 barometric pressure is that the percentage of haemoglobin and of 

 red corpuscles in the blood rises (see Chapter XIII). In different 

 individuals the rise varies considerably. Thus in persons who had 

 been living for some weeks on the summit of Pike's Peak we found 

 that the haemoglobin percentage varied from 113 to 153 per cent 

 of the normal. The rapidity with which the change occurs varies 

 also greatly in different individuals. Figure 72 shows the rate 



