CARBONIC ACID 157 



is about 0.000000044 N. This value is sub- 

 ject to constant slight variations, diminish- 

 ing as the blood passes through the lungs, 

 increasing during the greater circulation; but 

 variations of this kind are certainly very 

 slight in the healthy organism. The value 

 corresponds to a concentration of bicarbonates 

 about ten times as great as that of free car- 

 bonic acid. Together the acid and its salts 

 make up the larger part of all the carbonic 

 acid, and a very considerable fraction of all 

 the dissolved molecules of the blood. In 

 disease, especially diabetic coma, the hydro- 

 gen ion concentration may rise to 0.0000001 N, 

 or perhaps higher ; when acid is injected into 

 the blood the value may be greater still, but 

 death speedily ensues, and it is certainly im- 

 possible during life that there should be any 

 considerable permanent variation. 



Increase in acidity of the blood can occur 

 only in association with marked diminution 

 in the concentration of bicarbonates, which 

 may fall to less than one third of their normal 

 amount, greatly impoverishing the blood in 

 respect to carbonic acid, and interfering with 

 its excretion. This is due to the fact that 

 the amount of free carbonic acid in the blood 

 is under the independent control of the respira- 

 tory center, and when acids decompose bicar- 



