CHAPTER IV. 



THE BLOOD (continued). 



DESCRIPTION OF CERTAIN METHODS OF EESEARCH. 

 Determination of the Specific Gravity of the Blood. 



EXCEPT by operating with extreme expedition and at temperatures 

 below C. it would be quite impossible to determine the specific 

 gravity of the uncoagulated blood. It is obvious, however, that the 

 specific gravity of defibrinated blood can only differ very slightly 

 from that of blood which has not yet coagulated. It is therefore 

 usual to take the specific gravity of defibrinated blood as sufficiently 

 representing that of the blood. 



In the case of blood, this is best done with the aid of a specific 

 gravity bottle, of which two forms are represented in the annexed 

 woodcuts (Figs. 28 and 29). 



The flask is first weighed when empty ; then when filled with 

 distilled water at a known temperature ; the distilled water being 

 then poured out and the flask dried, the bottle is filled with 

 defibrinated blood at the same temperature as the water, and again 

 weighed. By these operations we ascertain the weight of the water 

 and of the blood respectively which at a given temperature are con- 

 tained in the bottle. 



Let a be the weight of the water contained in the flask, and b that 

 of the defibrinated blood ; then the specific gravity of the latter, 

 designated by d, will be 



a ' 



It is however very inconvenient to be obliged to weigh liquids at one 

 particular temperature, and if we have at our disposal a specific gravity 

 bottle such as is represented in fig. 29, arid a table of the density of water 

 at various temperatures, we can readily ascertain the specific gravity of the 

 blood, though its temperature be not exactly the same as that of the water 





