474 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



solution is added to blood instead of water, the corpuscles shrivel up and 

 therefore favor the reflection of light and prevent its transmission ; 

 hence the blood is now less transparent, but appears lighter in reflected 

 light (Fig. 174). 



The red blood-corpuscles are almost fluid in consistence, and 

 resemble, therefore, suspended drops of jell}'. This characteristic is 

 frequently seen when the circulation in the capillaries, as in the mesen- 

 tery of the guinea-pig, is examined under the microscope. The red 

 blood-cells will often be observed to change their shape by pressure 

 from a disk to an elongated rod, and sometimes such a distorted cor- 

 puscle will catch at the point of 

 bifurcation of a capillary, where it 

 may hang like a pair of saddle-bags, 

 part in one branch of the capillary, 

 and the other half in the opposite. 

 Even in animals with nucleated red 

 blood-cells, like the frog, similar 

 change in shape may be seen ; the 

 red blood-cells may even be seen to 

 pass out through the walls of the 

 blood-vessels, becoming in the 

 process drawn out into a fine thread. 

 The red blood-corpuscles are 

 composed of the " stroma" and " hae- 

 moglobin." 



Early observers regarded the red 

 blood-corpuscle as a vesicular body 

 in which a cell-membrane inclosed 

 fluid contents ; at present it is be- 

 lieved to be composed of a semi-fluid 

 net-work or frame-work, the stroma, 

 denser at the periphery than at the 

 centre, in the meshes of which are inclosed the other constituents of the 

 cell. The stroma may be demonstrated by alternately freezing and 

 thawing the blood, which then loses its opacity and becomes a clear, 

 lake-colored fluid, the haemoglobin having left the corpuscles to pass into 

 solution in the plasma, and the stromata remaining as colorless bodies, 

 which sometimes retain the original form of the blood-cell, but usually 

 are either more globular or more shriveled than normal. The stroma is 

 colorless and highly elastic and is albuminous in nature ; it is insoluble 

 in serum, dilute salt or sugar solutions, and water below 60 C., but it 

 is soluble in serum containing alcohol, ether, or chloroform, in caustic 

 alkalies, and in solutions of alkaline salts of the bile acids. 



FIG. 175. H^MOG^OBIN CRYSTALS 

 THE Ox. (Ellenberger.) 



OF 



