352 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



3. White Globules. — The function of the white globules 

 is much more obscure. In some way little understood 

 they seem to vitalize the blood, for, as already seen, 

 they are really living protozoa. It will be remembered 

 (page 329) that as soon as these enter the chyle in the 

 mesenteric glands this fluid becomes endowed with the 

 property of coagulation. Again, it is believed that these 

 globules act as scavengers of the blood, removing mi- 

 crobes and other offending substances by inclosing and 

 devouring them after the manner of rhizopods (page 

 346). Again, as already seen, these corpuscles crawl 

 about and change their shape like amoeba. When the 

 blood stagnates, as in inflammation, they actually squirm 

 themselves through the thin walls of the capillaries, and 

 wander about in the tissues; and, in case of breaking 

 down of the tissues and the formation of pus, they prob- 

 ably become the characteristic pus corpuscles. 



Origin and Life History of Blood. — 1. Plasma, as 

 already explained, is essentially the sanguified and vital- 

 ized peptones. Sugar is also taken up into the blood, 

 and in so far as it remains there is a constituent of the 

 plasma ; but normally there is only a trace of sugar in 

 the blood of the general circulation, because it is quickly 

 burned up. We shall speak of this more fully in another 

 place. 



2. White Globules, or Leucocytes. — We have already 

 seen that these are formed in the mesenteric glands; 

 but these are only lymphatic glands situated in the mes- 

 entery. Leucocytes are formed in all lymphatic glands 

 wherever situated and at all times,' whether chyle be 

 passing through them or not. They are also formed in 

 the spleen, for the blood of the splenic vein before it 

 enters the vena porta is ten to twenty times richer in 

 leucocytes than that of the general circulation. It 

 seems certain, then, that the leucocytes are formed in 



