PRIMARY FUNCTIONS OF THE ORGANISM 29 



movement. The actual basis for these creeping 

 movements is thus the contractility of the protoplasm 

 constituting the cell. 



In the course of these creeping or " amoeboid " 

 movements the leucocyte may encounter a bit of 

 worn-out tissue or 

 a vagrant bacterium. 

 It then throws out 

 pseudopodia on both 

 sides of the object, 

 which flow around it, 

 meet beyond, and thus 

 swallow into the body 

 of the cell the bac- 

 terium or tissue-frag- 

 ment, together with 

 a little drop of the 

 fluid in which both 

 are floating. (The 

 bacterium has been 

 ingested.) While in- 

 side the cell-body of 

 the leucocyte, certain 

 changes are induced 

 in such a particle by 

 products secreted by 

 the leucocyte that 



tend to dissolve or digest it. That part which 

 cannot be so digested is removed by the reversal 

 of the process employed in swallowing it, i.e. the 

 leucocyte creeps on and leaves it behind, it is 



FIG. 8. Phagocytes (leucocytes) 

 from the coelomic fluid of the earth- 

 worm : A, agglomeration of phagocytes 

 surrounding a foreign body ; B, single 

 leucocyte, with vacuoles. (From Sedg- 

 wick and Wilson, after Metchnikoff .) 



