BLOOD. 167 



Benzoate of soda. 



Margariii. 



Oleiii. 



Copper. 



Manganese. 



Silica. 



Oil the methods of analysing the blood. 



Although many of the proximate constituents of the blood 

 may be recognized without difficulty, there are some (especially 

 those which exist in only minute quantity) that cannot be 

 readily detected. An exact quantitative analysis of the blood, 

 including the determination of all the substances in the fore- 

 going table, would, in the present state of chemistry, be almost 

 an impossibility ; we must, therefore, content ourselves with the 

 quantitative determination of the more important constituents, 

 and arrange and determine the others, as, for instance, the 

 fats, salts, extractive matters, &c, in groups. For this purpose 

 fresh blood must be used : the clot must be allowed to sepa- 

 rate from the serum, and the two (the clot and the serum) must 

 then be analysed separately. 



The following method is given by Berzelius.^ Two known 

 quantities of blood are taken, one of which is allowed to coagu- 

 late spontaneously, while the other is evaporated for the pur- 

 pose of ascertaining the quantity of water. The clot, when 

 thoroughly separated, is removed from the first of these quan- 

 tities, cut into pieces, and placed upon an open weighed filter, 

 resting upon several folds of blotting paper ; it must then be 

 covered with a similar weighed filter, over which some more 

 blotting paper must be placed, and the whole must be compressed 

 by a stone or other weight. The blotting paper must be changed 

 as long as any moisture is communicated to it, and the clot 

 must be subsequently dried in vacuo over sulphuric acid, and 

 carefully weighed. By deducting the known weight of the 

 filters we obtain that of the fibrin and blood-corpuscles. 



The dried clot must now be frequently washed with water 

 at from 75° to 85°, until the fibrin is left colouiiess. 



The dried blood which has been used for the purpose of as- 

 certaining the quantity of water must be successively treated 



' Tliierchemie, p. 93. 



