GENERAL PROPERTIES: THE CORPUSCLES. 417 



The reservoir of alkali contained in the blood-plasma and 

 blood-corpuscles as sodium bicarbonate, dipotassium phosphate, 

 and the alkaline salts of protein constitutes what is known as the 

 alkali reserve. So long as this holds out the blood is able to pro- 

 tect its reaction when CO2 or fixed acids are added to it. It consti- 

 tutes, moreover, as we shall see, an agency by means of which 

 the CO2 constantly formed in the body is transported to the lungs 

 for excretion, with almost no increase in the hydrogen ion concen- 

 tration of the blood. 



Acidosis. — The actual reaction of the blood, as stated above, 

 does not vary much even under markedly pathological conditions, 

 but the amount of fixed acids added to the blood as a result of 

 the processes of metabolism may vary widely and may be greatly 

 increased under certain pathological conditions, diabetes for ex- 

 ample. While such an increase in the acids added to the blood 

 may not change its actual reaction perceptibly, owing to the pro- 

 tective mechanisms described, it will tend, of course, to reduce the 

 amount of protective sodium bicarbonate, since these acids will 

 combine with the sodium and drive off the CO2, which is then re- 

 moved by the lungs. The result in such cases is a diminution in 

 the amount of alkali in the blood available for the protection of 

 the reaction, or as it is frequently expressed, a diminution in the 

 alkaline reserve of the body. Such a condition is designated as 

 "acidosis," although the reaction of the blood is still alkaline. 

 Two relatively simple reactions have been suggested to test for the 

 existence of "acidosis." One is to determine the capacity of the 

 blood-plasma to absorb CO2 under a given pressure. The normal 

 CO2 capacity is from 50 to 60 per cent, and a decided fall below this 

 level indicates a diminution in alkaH in the blood. The second is to 

 ascertain the amount of, sodium bicarbonate given by mouth that 

 suffices to give an allcaline reaction to the urine. In acidosis more 

 carbonate will be required to give this result.* 



Specific Gravity. — The specific gravity of human blood in the 

 adult male may vary from 1.041 to 1.067, the average being about 

 1,055. The most satisfactory method of determining this factor is, 

 of course, to compare the weight of a known volume of blood with 

 that of an equal volume of water, but for observations upon human 

 beings such small quantities of blood must be used that recourse must 

 be had usually to a more indirect method. Perhaps the simplest of 

 the methods suggested is that devised by Hammerschlag. t In this 

 method a mixture is made of chloroform (sp. gr., 1.526) and benzol 

 (sp. gr., 0.889). The mixture is made in such proportions as to 



* See L. Henderson, "Science," July 27, 1917; Sellards, "The Principles of 

 Acidosis," 1917; and Van Slyke and Cullen, Loc. cit. 



t Hammerschlag, "Zeitschrift f. klin. Med.," 20, 444, 1892. 



27 



