92 APPLIED PHYSIOLOGY 



sumably of a protein nature, thrown off by the fixed 

 cells, which act as protectives against infection, and, 

 reasoning from analogy, it seems not unlikely that the 

 normal proteins of the blood may have a similar 

 origin. 



The salts of the plasma are chiefly the chloride, 

 carbonate and phosphate of sodium, the two latter being 

 responsible for the reaction of the blood, a matter 

 which must now be considered more closely. 



From a strictly chemical point of view the blood is 

 really an acid fluid, for the phosphates and bicarbonates 

 which it contains are really acid salts, inasmuch as they 

 still contain hydrogen atoms replaceable by a base.* 

 The blood is generally regarded as alkaline, however, 

 because its chief salts are alkaline to litmus, and it will 

 be convenient still to speak of it as alkaline. Quanti- 

 tatively considered, the alkalinity of the whole blood is 

 equal to 300 milligrammes of NaOH per 100 c.c., and this 

 degree of alkalinity is maintained with extraordinary 

 constancy, although a slight rise in it can be detected 

 after meals. In disease the alkalinity is probably never 

 increased, but it is occasionally diminished when large 

 quantities of acid are entering the circulation e.g., in 

 diabetic coma, and also in anaemia. The mechanism 

 by which this constancy of reaction is maintained is 

 interesting. Alkaline compounds entering the blood are 

 apparently partly excreted by the kidneys, carrying with 

 them a certain amount of water, so that they act as 

 diuretics, and partly turned out of the blood-stream into 



* It is interesting to note that the blood is really neutral by 

 physical methods of investigation, 



