290 



THE BLOOD. 



of dye which the protoplasm takes which determines the variety 

 of the corpuscles ; the nuclei of all the leukocytes is basophil. 



Composition of Leukocytes. The chemical composition of 

 leukocytes is given (Lilienfeld) as follows : 



Water . . I . 88.51 



Solids 11-49 



The solids are : 



Proteid 1.76 



Nuclein 68.78 



Histon (i. e., proteid part of the 

 nucleoproteid ) 8.67 



100.00 



Lecithin 7 51 



Fat 4.02 



Cholesterin 4.40 



Glycogen . 0.80 



This analysis of the cells is of those from the thymus, but we 

 are justified in concluding that the colorless corpuscles of the 

 blood which originate from lymphoid structures have a similar 

 composition. It is, however, impossible to investigate the color- 

 less blood-corpuscles by macrochemical methods. Micro-chem- 

 ically they can be shown to contain fat and glycogen (Halli- 

 burton). 



Functions of the Colorless Corpuscles. The movements which 

 occur in protoplasm, known as ameboid movements, have been 

 already described (p. 24). This power is possessed by the leuko- 

 cytes, by virtue of which they pass through the walls of the capil- 

 lary blood-vessels, this power being diapedesis or migration. 

 There is no doubt that this occurs normally to a certain extent, 

 but to a much greater extent under abnormal conditions, as in in- 

 flammations. When these migrated leukocytes accumulate out- 

 side the blood-vessels, and have lost their vitality, they consti- 

 tute pus. 



Phagocytosis. Metschnikoff has advanced the theory that 

 one of the important functions of the leukocytes is to ingest and 

 digest bacteria ; this constitutes phagocytosis. In this process the 

 polynucleated cells are the most active. There is no doubt that 

 by virtue of their ameboid movement the leukocytes do surround 

 and take into their protoplasm foreign matter, and if bacteria are 

 present they are likewise ingested, but whether they are thus 

 taken in while in a living state and destroyed, or only after their 

 vitality has left them, is a question. Those who favor the theory 

 look upon the leukocytes as the protectors of the human race 

 against the incursions of infectious diseases, if their vitality is 

 sufficient to overcome and destroy the bacteria of these diseases ; 

 whereas if the bacteria are the more powerful, then the disease 

 obtains a foothold. A person is said to be immune when on ex- 

 posure to a communicable disease, such as scarlet fever, measles, 

 etc., he does not contract it, and the explanations which have been 



