BLOOD SYSTEM. 



353 



the lymphatic glands and in the spleen, and that the 

 blood receives them while passing through these organs. 

 How they disappear is not certainly known. Possibly 

 they break up into so-called blood plates. 



3. Red Globules. — These are constantly changing ; 

 they have, like all living things, a definite life history ; 

 they are born, mature, decay, and die. If the body is 

 depleted of blood it quickly recovers its supply. If the 

 blood of another animal be transfused into the veins of 

 a man, at first two kinds of globules may be seen in the 

 blood, but as time goes on the animal globules decrease 

 and the human increase until only the human remain. 

 The red globules are therefore being renewed all the 

 time. Where do they come from ? At one time they 

 were thought to be transformed leucocytes ; but this is 

 probably not true. It is now believed that they are 

 formed in the red marrow of the bones, and perhaps also 

 in the spleen, by the division of certain large cells ob- 

 served there. This is their birthplace. Their active life 

 is in the circulation, doing their work of oxygen carry- 

 ing. Their death place is probably the liver and the 

 spleen. 



Briefly, then : 



Leucocytes are born in the lymphatics and the spleen. 



Red globules are born in the bones and the spleen. 



Red globules die in the liver and the spleen. 



It would seem, then, that the spleen has many and 

 important functions, but that it shares all these with 

 other organs. May not this explain the singular fact 

 that, although so important, yet it has been extirpated 

 in the dog without immediate serious injury to health. 



Now the blood goes everywhere, touches every tissue 

 and every cell. (1) It carries food, and thus becomes 

 the all-nourisher. (2) It takes up all waste and carries 

 it to the appropriate organ of elimination, and thus be- 



