THE CONTROL OF THE RESPIRATION 381 



anoxemia that causes the symptoms of mountain sickness and many of 

 these of pathological conditions such as pneumonia or CO-poisoning. 

 The only possible treatment is to raise the- tension of oxygen in the 

 alveolar air sufficiently to force some into solution in the plasma (see 

 page 445). 



After a time acclimatization to anoxemia occurs because of adjustments 

 which bring C H back to its normal value. These depend on excretion of 

 the excess of alkali by the kidneys and the conversion of a greater pro- 

 portion of ammonia into urea (page 650). Hasselbach and Lindhard, 60 

 Collip and Backus, 79 and Grant and Goldman 80 were the first to show 

 that CH of the urine becomes reduced early in anoxemia, but returns to 

 the normal after acclimatization is established, and that the excretion 

 of ammonia is also relatively decreased but remains low even after ac- 

 climatization. Haldane, Kellas and Kennaway 59 have confirmed these 

 observations by showing that the titrable acid of the urine is reduced 

 by one-half, or more. Diminution in the NH 3 excretion is always ob- 

 served when the excretion of fixed alkali is increased in proportion to the 

 acid,* and it indicates that the function of the organs which are respon- 

 sible for conversion of NH 3 to neutral urea, must become stimulated as 

 a protection against the alkalosis. The question therefore arises whether 

 the relative decrease in the acid excretion by the kidneys (rendering the 

 urine more alkaline) runs parallel with the diminished production of am- 

 monia. It was found that the ratio of ammonia to acid rose markedly, 

 showing that the conversion of NH 3 into urea did not occur as promptly 

 as the increased excretion of alkali by the kidney. Part of this delay is 

 no doubt dependent upon the time required for the ammonia already 

 present in the blood and tissue fluids to be excreted before the increased 

 urea formation could become evident in the urine. The results as a 

 whole show that the kidneys (and liver) on the one hand, and the 

 respiratory center on the other, respond to changes in C H of the 

 blood which are far below those that can be detected by exist- 

 ing physical or chemical methods of measurement (Haldane). The 

 respiratory center constitutes the first line of defence against any change in 

 C H by increasing or decreasing the rate at which C0 2 is blown off from the 

 blood. The kidneys constitute a second defence by altering the ratio of 

 acid base whicfcthey allow to pass into the urine, andjhe liver and other 

 organs form a third line of defence by altering the amount of free "NH 3 

 which they permit to enter the blood. The readjustment of the alveolar 

 C0 2 and of the acid and ammonia excretions do not return to the normal 

 until some time after the subject has been breathing at normal barometric 

 pressure. This will be made evident by consulting Fig. 142-A. 



*Benedict and Nash have recently shown that it is solely in the kidneys that the ammonia 

 for these purposes is formed (page 563). 



