354 THE RESPIRATION 



Relationship Among Acidosis Conditions, Alveolar CO., and Respir- 

 atory Activity. — It will be plain that variations in the respiratory hor- 

 mone, whatever this may he, are associated with changes in the C0 2 

 content of the alveolar air. Closer examination has shown, however, 

 that this relationship is by no means always so simple as in the instances 

 just described, where increased respiration was found to he associated 

 with an increase in alveolar C0 2 . There are many cases where the re- 

 verse relationship obtains — namely, decreased alveolar C0 2 and hy- 

 perpnea. The whole question is very closely linked with that of the con- 

 trol 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 respiratory disturbances occur will be much better understood than 

 they are at present. On account of its great importance, 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 become developed under altered physiologic 

 conditions. 



We shall consider these conditions in the following order: (1) Con- 

 stancy of the alveolar C0 2 under normal conditions and during moderate 

 variations in barometric pressure. (2) The quantitative relationship 

 between an artificially induced increase in alveolar CO, tension (as by 

 breathing C0 2 -rich air) and the increased respiration. (3) The results 

 of these observations will demonstrate a very precise relationship to exist 

 between alveolar C0 2 tension and respiration, but if we proceed to repeat 

 the latter observations under conditions where the accumulation of C0 2 

 in the inspired air is accompanied by oxygen deficiency (as by breathing 

 in a confined space), we shall see that the relationship no longer holds, 

 indicating that the oxygen deficiency has caused something to happen 

 which disturbs it. 



We shall find that the disturbing factor is accumulation of unoxidized 

 acids in the blood, and this will naturally lead us to study the conditions 

 in which such acids might develop; namely, (4) Breathing in rarefied 

 air (mountain -sickness). (5) Apnea. (6) Muscular exercise. 



In succeeding chapters, Ave intend to review- the work in these fields in 

 considerable detail, partly because of its very important bearing on the 

 genera] question of the control of the respiratory center and partly be- 

 cause of the light the observations throw on the nature of the mechanism 

 involved in the adjustment of the C H of the blood and tissues. 



As we have seen, much work concerning the physicochemical principles 

 involved in the control of the reaction of the blood has been contributed 

 during recenl years by physical and biological chemists, but much of this 



