48 IMMUNITY 



Amoeba and certain other unicellular vegetable organisms 

 belonging to the myxomycetes possessing amoeboid properties and 

 having the faculty of throwing out pseudopodia or protoplasmic 

 arms, acquire their food by enveloping smaller organisms and 

 other nutritious matter which they absorb. Certain intracellular 

 ferments, which they possess, digest fibrin and gelatine, and con- 

 vert starch into sugar. These cells protect themselves against 

 inimical microorganisms by enveloping and digesting them. 



FIG. 14. Phagocytosis. Gonococci in leucocytes in pus from gonorrhoea. 

 (Kolle and Wassermann.) 



They are attracted by food and moisture (called positive chemo- 

 taxis) and repelled by strong solution of salt, poisons, etc. (nega- 

 tive chemotaxis) . 



Higher in the animal scale among the multicellular organisms, 

 the cells of the intestines have the property of absorbing and di- 

 gesting food. These fixed cells are called sessile phagocytes. 

 Still higher in the scale (man) certain digesting cells are present 

 in the digestive tract, which are incapable of absorbing food. 

 They, however, secrete ferments which digest gelatine and fibrin, 

 and convert starch into sugar. But other cells of the animal ' 

 body, the leucocytes, large mononuclears and certain fixed tissues- 

 cells, have the property of engulfing foreign bodies like bacteria 



