QUANTITY AND COMPOSITION OF BLOOD 971 



graduated series of these mixtures is kept in bottles and their specific 

 gravity is generally determined before the experiment. Hammer- 

 schlag's method consists in placing a drop of blood in a mixture of 

 chloroform and benzene and then adding chloroform or benzene, as 

 the case may be, until the drop neither rises nor falls. The specific 

 gravity of the mixture is then taken. The specific gravity varies 

 in man between 1057 and 1066, and in woman from 1054 to 1061. It 

 is increased by loss of water, as after profuse perspiration, or by passive 

 congestion of the part from which the sample is taken. It is also 

 increased as a result of any operation upon a serous cavity in con- 

 sequence of exudation of plasma in the inflamed or irritated part. It 

 is diminished as the result of bleeding. The specific gravity of serum 

 is 1028 to 1032, of corpuscles about 1090. It is interesting to note 

 that the specific gravity of the blood is highest in the foetus at full 

 term, when it amounts to 1066, contrasting with that of the mother 

 at the same time, the specific gravity of whose blood is only 1050. 

 The specific gravity rapidly falls to the latter figure after birth. 



THE REACTION OF THE BLOOD 



The blood is alkaline to litmus. This fact can be demonstrated 

 by allowing a drop to fall on a piece of glazed litmus paper and then 

 wiping away the blood with a piece of linen moistened with distilled 

 water or neutral saline solution. In order to estimate the alkalinity 

 a small definite quantity of the blood is mixed with sulphate of soda 

 solution containing a definite amount of tartaric acid. The acid 

 mixture is then titrated against a decinormal solution of sodium 

 hydrate until the mixture gives a blue stain when a drop of it is placed 

 on glazed litmus paper. The alkalinity of normal blood as deter- 

 mined in this way amounts on the average to 0-2 grm. NaHO per 

 100 c.c. of blood. If the blood be laked the alkalinity rises to as much 

 as 04 grm. NaHO per 100 c.c. 



All these questions of reaction depend, however, on the indicator 

 employed. A neutral salt might react alkaline to litmus if the acid 

 radical of the salt were capable of being displaced by the coloured 

 acid radical of the indicator with the production of a blue alkaline 

 salt of litmus. Sodium bicarbonate may be acid or neutral to 

 litmus and alkaline to methyl orange. The absolute alkalinity of 

 any fluid may be expressed by the number of free OH ions 

 which it contains, just as the acidity is a measure of the free H 

 ions. The number of free OH ions in the blood can be determined by 

 an electrical method, and is found to be very small, very little more in 

 fact than that contained in distilled water. The alkalinity of the blood 

 as ordinarily determined by the litmus method gives us, however, more 

 important knowledge than this determination of its absolute alkalinity, 



