CHAP. XXVII.] THE CONSTITUTION OF THE BLOOD. 291 



of large size, as the common frog, be passed through filtering 

 paper, its liquid portion passes through, leaving the coloured 

 particles upon the filter : thus analyzing the blood into two parts 

 the liquor sanguinis and the blood particles. The former, by 

 the spontaneous coagulation of the fibrine, quickly separates into 

 serum and fibrine, which in this instance is colourless, but in the 

 ordinary coagulation it is more or less coloured by the red parti- 

 cles, which become entangled by the coagulating fibrine. Another 

 mode of effecting a similar analysis is that suggested by Dr. A. 

 Buchanan of Glasgow : it consists in mixing fresh-drawn blood 

 with six or eight times its bulk of serum, and filtering through 

 blotting-paper : coagulation is retarded by the admixture with 

 serum, and a great part of the diluted liquor sanguinis passes 

 through the filter, and subsequently coagulates. By microsco- 

 pical analysis of the blood, we find, that, besides the red particles, 

 it contains others which are devoid of colouring matter namely, 

 the colourless corpuscles. 



The constitution of the blood is expressed by the following 

 table : 



( Corpuscles; red and colourless. 

 The blood consists of < ^ fibrine 



(liquor sanguinis, consisting of-j 



' serum. 



That the blood has the same essential characters in both the 

 vertebrate and invertebrate classes has been shown by Mr. Whar- 

 ton Jones's researches, who finds the coloured and colourless 

 corpuscles in the blood of all animals, presenting, however, suffi- 

 ciently distinctive features. 



In man and the mammalia, there are two kinds of blood, dis- 

 tinguished by difference of hue, the scarlet, arterial blood, obtained 

 from the left side of the heart, and from the arteries : and the 

 black, or dark red, venous blood, obtained from the right side of the 

 heart, and from the systemic veins. We shall consider, further 

 on, the special characters of each kind, and the cause of their 

 differences. 



The temperature of the blood ranges between 100 and 105. 

 Its reaction is slightly alkaline, so that a drachm of blood will 

 saturate rather more than a drop of vinegar. 



The consideration of the natural history of the human blood 

 involves the determination of the following points : 



First, the quantity of blood in the body. 



Secondly, the phenomenon of coagulation, and the circumstances 

 which promote or retard it. 



