394 BLOOD AND LYMPH. 



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. 408) 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-h and OH , or sub- 

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

 by reaction with water. 



In a solution of sodium carbonate we may assume that some of the 

 molecules dissociate into the ions Na -j-, Na -(-, and CO 3 =, and that the anion, 

 CO 3 =, reacts with the dissociated molecules of water, H -)-, HO , giving 

 HCO 3 and OH . There will be present in the solution, therefore, the 

 following ions, Na -f, OH , and Na -f-, 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 , cannot 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 4- to combine with the OH , but its own anion will combine 

 with all of the dissociated Na -f ', consequently more Na 2 CO s 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 necessary to make use of the methods of physical 

 chemistry. Those who have employed these methods f report that olood 

 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 reaction. In fact, the sodium in the blood 

 behaves substantially as if it were present as the bicarbonate, NaHCO 3 , 

 whose dissociation 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 variations in the amount of alkali, Na, in combination with weak acids, 

 such as carbonic or phosphoric acid or with the blood-proteins. The results 

 represent what has been called the "titration alkalinity" of the blood and 

 are useful in the information they furnish regarding the capacity of the blood 

 to carry carbon dioxid (see Respiration), or to neutralize the acid products 

 formed during normal metabolism and especially during the abnormal metab- 

 olism of many diseased conditions. 



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. 



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

 Hober, ibid., 99, 572. 



