472 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



In man and all mammalia, with the exception of the camel tribe, 

 they are circular and devoid of a nucleus ; in birds, reptiles, and most 

 fish, they are oval, biconvex, and nucleated ; in the camel, the red 

 blood -cells are oval, but are not nucleated. From the fact that the 

 edges of the red blood-cells are convex and the centre concave, these 

 different parts refract light differently, and when examined under the 

 microscope, if the edges are sharply denned, the centres appear dark, 

 and vice versa (Fig. 172). 



There is no constant relation between the size of an animal and the 

 size of its blood-disks ; thus, among mammals, although the red blood- 

 corpuscles of the elephant are the largest, those' of the mouse are by no 

 means the smallest, being, in fact, three times as large as those of the 

 musk-deer (Fig. 173). 



FIG. 172. RED BLOOD-CORPUSCLES. (Landois.) 



A, human red blood-corpnscles: 1, seen on the flat; 2, on edge: 3, rouleaux of colored corpuscles 

 slightly separated. B, colored amphibian blood-corpuscles: 1, seen on the flat, and, 2, on edge. C, ideal 

 transverse section of a human red blood-corpuscle magnified five thousand times linear: no, diameter; 

 c d, thickness. 



In the various domestic animals their diameter is placed as follows 

 in fractions of a millimeter : horse, 0.004-0.005 ; ox, 0.003-0.005 ; dog, 

 0.005-0.007; sheep, 0.002-0.004; goat, 0.002; hog, 0.003-0.004 milli- 

 meters. Frequentl}', particularly in growing animals and after profuse 

 hemorrhage or exhausting disease, red blood-corpuscles smaller than the 

 above will be found. These are probably to be regarded as young, grow- 

 ing blood-cells. The number of the red blood-cells is almost infinite; in 

 one cubic centimeter of blood in man, five million red blood-disks have 

 been estimated to be present ; in the goat, nine to ten millions ; in the lamb, 

 thirteen to fourteen millions ; in birds, one to four millions ; in the fish, 

 one-quarter to two millions ; in the frog, half a million ; and in the pro- 

 teus, thirty-six thousand. In fact, 30 to 40 per cent, of the entire mass 

 of the blood is composed of red blood-corpuscles ; thus, in the horse, 



