12 AMCEBA 



Finally, the Amoeba as it creeps slowly on leaves this empty 

 cell-wall behind, and thus gets rid of what it has no further 

 use for. It is thus able to ingest living organisms as food ; 

 to dissolve or digest their protoplasm ; and to egest or 

 get rid of any insoluble materials they may contain. Note 

 that all this is done without either ingestion aperture (mouth), 

 digestion cavity (stomach), or egestion aperture (anus) ; the 

 food is simply taken in by the flowing round it of pseudopods, 

 digested as it lies enclosed in the protoplasm, and got rid of 

 by the Amoeba flowing away from it. 



It has just been said that the protoplasm of the prey is 

 dissolved or digested : we must now consider more particu- 

 larly what this means. 



The stomachs of the higher animals ourselves, for 

 instance produce in their interior a fluid called gastric 

 juice. When this fluid is brought into contact with albumen 

 or any other proteid a remarkable change takes place. The 

 proteid is dissolved and at the same time rendered diffusible, 

 so as to be capable, like a solution of salt or sugar, of passing 

 through an organic membrane (see p. 6). The diffusible 

 proteids thus formed by the action of gastric juice upon 

 ordinary proteids are called peptones : the transformation 

 is effected through the agency of a constituent of the gastric 

 juice called pepsin. 



There can be little doubt that the protoplasm ot Amoeba 

 is able to convert that of its prey into a soluble and diffusible 

 form, possibly by the agency of some substance analogous 

 to pepsin, and that the dissolved matters diffuse through the 

 body of the Amoeba until the latter is, as it were, soaked 

 through and through with them. Under these circumstances 

 the Amoeba may be compared to a sponge which is allowed 

 to absorb water, the sponge itself representing the living 

 protoplasm, the water the solution of proteids which per- 



