READJUSTMENTS OF REGULATION 41 



disturbances which physiology has to deal with are far 

 more minute than those which are appreciable by 

 chemical methods, so that exact regulation of the 

 reaction of the blood is indispensable. 



We have seen above that the composition of the 

 blood is so regulated that not only is its reaction 

 practically constant, but the volume of C0 2 taken up 

 by a given volume of blood at a given pressure of CO, 

 remains also the same under ordinary normal condi- 

 tions. It is easy, however, to disturb this regulation 

 temporarily. One means of doing so is by violent 

 muscular exertion. Douglas and I found that a few 

 minutes after violent exertion the volume of C0 2 

 taken up by a given volume of human arterial blood 

 was reduced to about half. An hour later, however, 

 the blood was again normal. The reduction was 

 probably due to excessive discharge of lactic acid into 

 the blood : for not only was the resting alveolar CO, 

 pressure diminished, but Ryffel succeeded in showing 

 that after similar violent exertion the proportion of 

 lactic acid in the blood and urine is greatly increased. 

 RyfTel showed also that this excess disappears in about 

 an hour, which is the same time, as we had observed, 

 that the alveolar C0 2 pressure requires to rise again to 

 normal after a violent exertion. It is clear, however, 

 that the capacity of the blood for taking up C0 2 can- 

 not depend merely on its reaction, and must depend on 

 the presence in regulated amount of all the various sub- 

 stances including albuminous substances, which enter 

 into chemical reaction when CO, is present. Their 

 amount must therefore be regulated — probably by the 



