THE BLOOD 77 



blue the alkaline reaction. To phenolphthalein blood is neutral, for 

 this reagent cannot decompose the carbonates. Blood can take up 

 a certain amount of acid before it begins to react acid. This is 

 because it contains carbonates (" buffer salts ") and proteins which 

 combine with the acid. It is for this reason that it is difficult to ascer- 

 tain the reaction of the blood by chemical means. Titrating with acid, 

 the amount of neutralizable alkalinity is obtained, alkali being liberated 

 in the process from the proteins and by dissociation of the carbonates 

 {Na 2 CO 3 , NaHC0 3 ) and the phosphates (Na 2 HPO 4 ). This neutralizable 

 alkali usually equals 350 to 400 milligrammes NaHO per 100 c.c. 

 But the real alkalinity, as measured by the electrical method, is due 

 to free OH ions, and these are usually present in .a concentration 

 little greater than in water. Na 2 C0 3 in aqueous solution is dissociated, 



more or less, into the ions 2Na and C0 3 . Some of the C0 3 ions com- 



+ 



bine with H ions of the dissociated water, forming HC0 3 , and HO ions 

 are thus set free to produce the alkaline reaction. On adding acid 



these HO ions are removed, and, the equilibrium being disturbed, 

 more Na 2 CO 3 is dissociated, and this goes on until all the Na 2 C0 3 is 

 dissociated. The alkali existing as salts, carbonates, and phosphates, 

 is known as diffusible alkali; that combined with protein is termed 

 non-diffusible alkali. As the corpuscles are richer in diffusible alkali 

 than the plasma, the number of corpuscles modifies the amount 

 of neutralizable alkali. 



On passing carbon dioxide gas through blood, the loose combination 

 between alkali and protein of both the plasma and corpuscles is split 

 up, and sodium carbonate partly formed. C0 3 ions pass from the 

 corpuscles into the plasma, and Cl ions from the plasma into the 

 corpuscles, and as the sodium carbonate in the plasma is increased, so 

 is the neutralizable alkalinity. 



It is very difficult to affect the reaction of the blood by swallowing 

 acids. Two drachms of official hydrochloric acid taken with food 

 have no effect upon the reaction of the blood, because the acid com- 

 bines with the proteins of the food, etc. ; two drachms of tartaric acid, 

 on the other hand, may diminish the neutralizable alkalinity. These 

 acids combine with the bases and form salts which are little disso- 

 ciated. 



Acids entering the blood are neutralized by combination with 

 ammonia, a product of protein katabolism, or by union with bases of 

 the carbonates, carbonic acid being expired. Alkalies are neutralized 

 by the carbonic acid produced in the body. The blood is thus kept 

 neutral while the amount of acid or alkali passing into it varies 

 considerably. Muscular exertion diminishes the titration alkalinity 

 owing to the production of lactic acid. The concentration of the 

 H ions in the blood regulates the activity of the respiratory centre; 

 lactic acid and carbonic acid are both produced on exertion, and their 

 cumulative effect produces dyspnoea. The " buffer salts " help to 

 regulate this. 



