82 THE BLOOD 



4. Eosinophile cells, like the last, but with cytoplasm filled 

 with coarse granules. 



It is possible that the members of the last classification 

 may be progressive stages in the growth of a single kind of 

 cell, the lymphocyte forming the youngest, while the poly- 

 nuclear cell forms the oldest stage. Leukocytes show ameboid 

 movements which enable them to move from place to place 

 (therefore called wandering cells), and even to pierce the walls 

 of the bloodvessels and get into the lymph spaces This process 

 is known as diapedesis. Their number is put at about 7500 

 per c.mm. A marked increase in number (leukocytosis) is seen 

 in leukemia. 



Function of Leukocytes. A number of suggestions have been 

 made as to this : 



1. They protect the body from disease by ingesting patho- 

 genic bacteria (phagocytosis). Such cells are known as phago- 

 cytes; or they may guard the body by the formation of protective 

 proteins which destroy disease germs and their toxins. 



2. They aid in the absorption of fats and peptones. 



3. They take part in the coagulation of the blood. 



4. They help to maintain the normal composition of the 

 blood in regard to its proteins, since the latter are not all formed 

 directly from absorbed food. They do this by undergoing dis- 

 integration in the blood and by active metabolic changes which 

 are indicated by their cytoplasm in the formation of zymogen 

 granules. Leukocytes multiply by karyokinetic division, and 

 are also newly formed in the lymph glands and lymphoid tissue. 



The blood plates are small circular or oval bodies of homo- 

 geneous structure and of variable size. Their number is about 

 250,000 per c.mm. They are not independent cells, and there- 

 fore soon disintegrate. Composed of the same substance as 

 the nuclei of leukocytes, they are often regarded as nothing 

 more. They take part in the coagulation of the blood. 



Plasma. The plasma, which is a viscid, straw-colored fluid 

 of a specific gravity of 1030, may be obtained in a number of 

 ways: The blood may be cooled, in which case coagulation 

 takes place slowly and the corpuscles have time gradually to 

 sink to the bottom of the vessel. The corpuscles having a 

 specific gravity of 1088 are the heaviest components of the 

 blood. When blood is received directly into neutral salt solu- 



