GENERAL PROPERTIES: THE CORPUSCLES. 383 



methods differ among themselves chiefly in the means used to 

 determine the point of neutralization of the blood by the acid 

 added. In some methods litmus is employed, in others lakmoid, 

 and in one (Dare's) the end-reaction is determined spectroscopically 

 on the belief that the characteristic absorption spectrum of oxy- 

 hemoglobin (p. 395) disappears at the point of neutralization.* 



In reference to this subject of the reaction of the blood and of the 

 tissues of the body generally a difference in terminology prevails 

 at present which tends to confuse the beginner. Some writers use 

 the term alkalinity in the sense of titration alkalinity to indicate 

 that the blood will neutralize a certain amount of weak acid added 

 to it. Others, however, employ the term in its strict sense, as 

 developed by modern physical chemistry, to indicate an excess of 

 hydroxyl ions (OH ). From the latter standpoint a solution is 

 alkaline when it contains a substance or substances which upon 

 dissociation yield an excess of hydroxyl ions, sodium hydroxid, 

 for example, which on dissociation gives Na+ and OH , or sub- 

 stances, such as sodium carbonate, which give rise to hydroxyl ions 

 by reaction with water. In a solution of this latter salt we may 

 assume that some of the molecules dissociate into the ions Na-h, 

 Na+ , and CO 3 = , and that the anion, CO 3 = , reacts with the disso- 

 ciated molecules of water, H+, HO , giving HCO 3 and OH . 



There will be present in the solution, therefore, the following ions, Na+, 

 OH , and Na+ , HCO 3 ; and the presence of the hydroxyl ion confers upon 

 the solution its alkaline reaction and properties. In such a solution of a 

 strong base with a weak acid the' alkalinity, that is, excess of OH , can not be 

 determined by titration with an acid stronger than carbonic acid. If tartaric 

 acid is added, for instance, the acid will not only give its H+ to combine with 

 the OH , but its own anion will combine with all of the dissociated Na+ ; 

 consequently more Na^C^ will be dissociated, and this reaction goes on, if 

 sufficient acid is used, until all of the sodium carbonate is destroyed. To 

 determine the excess of hydroxyl ions in such a solution as blood it is neces- 

 sary to make use of the methods of physical chemistry. Those who have 

 employed these methodsf report that blood contains no greater quantity of 

 hydroxyl ions than pure water, and must, therefore, be reckoned as a neutral 

 liquid. This conclusion is corroborated further by the fact that with some 

 indicators e. g., phenolphthalein the blood does not give an alkaline reac- 

 tion. In fact, the sodium in the blood behaves substantially as if it were 

 present as the bicarbonate, NaHCO 3 , a theoretically acid salt whose dis- 

 sociation would be represented by the two ions Na+, HCO 3 . The many 

 observations, therefore, which have been made by titration of the blood must 

 be considered as not giving its variations in alkalinity, but rather the varia- 

 tions in the amount of alkali, Na, in combination with weak acids, such as car- 

 bonate or phosphate. The results represent what has been called the "titra- 

 tion alkalinity of the blood. 



Specific Gravity. The specific gravity of human blood in the 

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



* For an account of these methods see Simon, "A Manual of Clinical Diag- 

 nosis," 1904. 



t Fraenckel, "Archiv f. d. gesammte Physiologic," 96, 601, 1903; and 

 Hober, ibid., 99, 572. 



