372 THE RESPIRATION 



cies include afferent nerve stimulation, lowering of the 2 -tension, or in- 

 crease in C H of the blood brought about by other acids than C0 2 such 

 as occurs in clinical cases of acidosis (see page 654). 



The whole question is very closely linked with that of the control of the 

 reaction of the body fluids and with the etiological factors in acidosis. 

 When it is fully answered, many obscure clinical conditions in which respi- 

 ratory disturbances occur will be much better understood than they are at 

 present. On account of the great importance of the subject, considerable 

 attention will be devoted in the next few pages to some of the researches 

 which have been made bearing on the relationship between the C0 2 of 

 the alveolar air and the various modified types of breathing that can be 

 produced experimentally or which become developed under altered physi- 

 ological conditions. 



Even at the risk of repetition let us consider what will happen when 

 excess of C0 2 is added to the blood in the body, either as a result of 

 respiring C0 2 -rich air or because of increased production of this gas in 

 the tissues, as in muscular exercise. The tension of C0 2 in the blood 

 will first of all increase and tend to raise CH since, as we have seen, this 



TT QQ 



depends on the molecular ratio - (where B HC0 3 stands for 



B HC0 3 



NaHC0 3 and other similar compounds). The excess of C0 2 will be re- 

 moved, partly by increased breathing and partly by basic substances, 

 including Na, being set free to combine with it. In these ways the 



TT p(") 



ratio ~ will tend to come back to its normal value but now with 



both free C0 2 and total bicarbonates absolutely greater than before, so 

 that the C0 2 combining power of the blood will be raised (page 42). 



On the other hand, when fixed acids are added to the blood they will 

 appropriate some of the base (B) and liberate H 2 C0 3 so that both the 

 tension of C0 2 and C H will rise (P H become less), equilibrium being then 

 reestablished by increased breathing and blowing off of C0 2 . If the 



increased breathing does not suffice in both these cases to restore the 



TT c*r\ 



normal J* J* ratio, other compensating mechanisms come into play, 

 B 



namely, increased excretion of acid by the urine and combination with 

 ammonia (page 381). 



When the H 2 C0 3 is lowered as by increased breathing, changes of an 

 opposite character occur and these will be discussed in the following 

 pages. 



