12 AMCEBA LESS. 



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 matorials they may contain. Note 

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

 digestive cavity (stomach), or egestive aperture (anus) ; the 

 food is simjjly taken in by the flowing round it of protoplasm, 

 digested as it lies enclosed in the protoplasm, and the useless 

 part 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 

 eflfected through the agency of a constituent of the gastric 

 juice called pepsin. 



There can be little doubt that the protoplasm of Amceba 

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

 form 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 proto- 

 plasm, the water the .solution of proteids which permeates it. 

 It has been proved by experiment that proteids are the only 

 class of food which Amoeba can make use of : it is unable to 



