BLOOD AND H^MOPOIETIC ORGANS 93 



the lymph spaces of the tissues.* Free acids or acid 

 salts are neutralized partly by the alkaline sodium 

 phosphate (Na 2 HP0 4 ) of the blood, which they convert 

 into sodium acid phosphate (NaH 2 P0 4 ), and which is 

 voided in the urine, and partly by the sodium carbonate 

 of the plasma with the liberation of C0 2 , which is 

 eliminated by the lungs. If there be more acid than 

 can be dealt with in this way, the excess appears to lay 

 hold of ammonium carbonate (probably in the liver), 

 diverting it from its usual fate of being turned into urea, 

 and converting it into an ammonium compound of the 

 corresponding acid which is excreted by the krdney. 

 A surplus of ammonium salts in the urine is therefore 

 an indication of the entry into the circulation of acid 

 compounds, one of the best examples of which is to be 

 found in diabetic coma, in which aceto-acetic acid is 

 excreted in such combination in enormous quantities. 

 So perfect is this mechanism that the reaction of the 

 blood remains largely independent of the amount of 

 acid entering the circulation. Thus, even a dose of 

 2 drachms of the official HC1 has no effect on the reaction 

 of the blood. On the other hand, an ounce of dilute 

 lactic acid when given in one day reduced the alkalinity 

 by one-fourth, whilst 2 drachms of tartaric acid reduced 

 it one-sixth (Freudberg).t 



The relative proportion of phosphoric and carbonic 

 acids in the blood depends very much upon the com- 

 position of the diet. The chief mineral constituents of 



* Hence it is that if bicarbonate of soda be given in large 

 quantity for some time e.g., in diabetes dropsy is apt to result, 

 t Vvrchow's Arcliiv, 1891, cxxv. 566. 



