CHEMICAL COMPOSITION. xxxiii 



the clot remains free from redness, and forms the well-known " buffy coat" 

 so apt to appear in inflammatory blood. Now, in such cases, a portion of 

 the clear liquor may be taken up with a spoon, and allowed to separate by 

 coagulation into its fibrin and serum, so as to demonstrate its nature. 

 Professor Andrew Buchanan has pointed out another method of separating 

 the liquor sanguiuis from the red corpuscles, which I have repeatedly tried 

 with success ; it consists in mixing fresh-drawn blood with six or eight times 

 its bulk of serum, allowing the red particles to subside, and then decanting 

 the supernatant fluid, and filtering it through blotting-paper ; the admixture 

 of serum delays coagulation, and a great part of the liquor sanguinis, of 

 course diluted, and usually more or less coloured, passes through the filter, 

 and subsequently coagulates. 



Coagulated plasma, whether obtained from buffy blood, or exuded on 

 inflamed surfaces, presents, under the microscope, a multitude of fine fila- 

 ments confusedly interwoven, as in a piece of felt ; but these are more or 

 less obscured by the intermixture of corpuscles and fine granules, the former 

 having all the characters of the pale corpuscles of the blood. The filaments 

 are no doubt formed by the fibrin, as it solidifies in the coagulation of the 

 liquor sanguinis. 



Blood may be freed from fibrin by stirring it with a bundle of twigs, 

 which entangle the fibrin as it concretes. 



CHEMICAL COMPOSITION OF THE BLOOD. 



The blood is slightly alkaline in reaction. Carbonic acid, oxygen, and 

 nitrogen gases may be extracted from it, by exhaustion (Magnus), by 

 heating after dilution with water (L. Meyer), or by both these means com- 

 bined (Setschenow). Carbonic acid is yielded in largest proportion, oxygen 

 next, and nitrogen least. The nitrogen appears to be simply retained by 

 absorption, the other two partly by absorption and partly by weak chemical 

 combination. The combined oxygen is probably in great part held by some 

 component of the red corpuscles ; the carbonic acid, which is obtained in 

 larger measure from serum, seems to be combined partly with carbonate of 

 soda in a bicarbonate, and partly with phosphate of soda, from both of 

 which combinations it can be set loose by heat and reduction of pressure. 

 Arterial blood yields more oxygen and less carbonic acid than venous 

 blood. 



On being evaporated, 1000 parts of blood yield, on an average, about 

 790 of water and 210 of solid residue. This residue has nearly the same 

 ultimate composition as flesh. A comparative examination of dried ox- 

 blood and dried flesh (beef), by Playfair and Boeckmann, gave the following 

 mean result : 



Flesh. Blood. 



Carbon 51-86 51 "96 



Hydrogen 7'58 7'25 



Nitrogen 15'03 15'07 



Oxygen 21'30 21'30 



Ashes " . 4-23 4'42 



Red Corpuscles. The specific gravity of the red corpuscles, in a moist 



c 



