68 THE BLOOD. 



dilution the corpuscles, as already said, may be made to swell 

 up, by absorbing the fluid ; and, if much water be added, they 

 will become spherical and pellucid, their coloring-matter being 

 dissolved, and, as it were, washed out of them. Some of them 

 may thus be burst; the others are made obscure; but many of 

 these latter may be brought into view again by evaporating, 

 or adding saline matter to, the fluid, so as to restore it to its 

 previous density. The changes thus produced by water are 

 more quickly effected by weak acetic acid, which immediately 

 makes the corpuscles pellucid, but dissolves few or none of 

 them, for the addition of an alkali, so as to neutralize the acid, 

 will restore their form though not their color. 



A peculiar property of the red corpuscles, which is exag- 

 gerated in inflammatory blood, and which appears to exist in 

 a marked degree in the blood of horses, may be here noticed. 

 It gives them a great tendency to adhere together in rolls or 

 columns, like piles of coin, and then, very quickly, these rolls 

 fasten together by their ends, and cluster ; so that, when the 

 blood is spread out thinly on a glass, they form a kind of ir- 

 regular network, with crowds of corpuscles at the several points 



corresponding with the knots of the 

 FIG. 25. net (Fig. 25). Hence, the clot 



formed in such a thin layer of blood 

 looks mottled with blotches of pink 

 upon a white ground ; in a larger 

 quantity of such blood, as soon as 

 the corpuscles have clustered and 

 collected in rolls (that is, generally 

 in two or three minutes after the 

 blood is drawn), they begin to sink 

 very quickly; for in the aggregate 

 Red corpuscles collected into they present less surface to the re- 

 roils (after Henie). sistance of the liquor sanguinis than 

 they would if sinking separately. 



Thus quickly sinking, they leave above them a layer of liquor 

 sanguinis, and this coagulating, forms a buffy coat, as before 

 described, the volume of which is augmented by the white 

 corpuscles, which have no tendency to adhere to the red ones, 

 and by their lightness float up clear of them. 



Chemical Composition of Red Blood-cells. 



It has been before remarked, that the red blood-corpuscles 

 are formed of a colorless stroma, infiltrated with a coloring 

 matter termed hcemoglobin. As they exist in the blood, they 

 contain about three-fourths of their weight of water. 



The stroma appears to be composed of a nitrogenous prox- 



