BLOOD, LYMPH, AND CHYLE 149 



having very thin walls. Within these vessels are found 

 colored nucleated cells, some of which become changed in 

 the marrow into unnucleated red disks which are swept 

 into the blood current. It is the important function of 

 the red corpuscles to take in oxygen from the air which 

 reaches the blood in the lungs, and carry it to the other 

 tissues of the body. The red corpuscle lives in the blood 

 for an unknown time. When it dies, a new one takes 

 its place. The spleen also is believed to aid in the manu- 

 facture of both the red corpuscles and the white, but we 

 have little positive knowledge upon the subject. 



206. The White Corpuscles are mostly larger than the 

 red, being generally about ^Vo .^ an ^ ncn * n diameter, 

 though some are smaller than the red. Some are globular 

 masses of granular protoplasm without cell walls and hav- 

 ing one or more nuclei. Others are of irregular and con- 

 stantly changing shape, less granular than the first and 

 with several nuclei. Many writers have remarked the 

 striking likeness of these corpuscles to the one-celled 

 animalcule, the amoeba. They have the same power as 

 the amoeba to change their shape spontaneously, sending 

 out processes from various parts of their circumference; 

 and they are able to take in and digest the bacilli which 

 are sometimes found in the blood, as the amo3ba digests 

 food. There are found in the blood some other small 

 bodies, whose nature and purpose are unknown. 



207. Chemical Composition of Blood. The blood is alka- 

 line, owing to the presence of small quantities of alkaline 

 salts. It contains chlorides, phosphates, and carbonates 

 of sodium and potassium, and smaller quantities of cal- 

 cium and magnesium. 



208. Clotting of the Blood. The blood in the blood ves- 

 sels is perfectly fluid, but if drawn out and allowed to 



