234 AMOEBA CHAP. 



swallowed, rendering it soluble and diffusible before it 

 passes through the epithelial cells of the enteric canal into 

 the blood : the gastric juice, for example, has the power of 

 converting proteids into peptones by means of the ferment 

 pepsin (p. 74) ; the digestion here takes place outside the 

 cells, i.e. is extracellular. There can be little doubt that 

 the protoplasm of Amoeba is able to render that of its 

 prey soluble and diffusible by the agency of some sub- 

 stance 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. The 

 process of digestion in Amoeba thus takes place within a 

 single cell, i.e. it is intracellular. 



It has been proved by experiment that proteids are the 

 only class of food which Amoeba can make use of: it is 

 unable to digest either starch or fat (p. 72). Mineral matters 

 must, however, be taken with the food in the form of a 

 weak watery solution, since the water in which the ani- 

 malcule lives is never absolutely pure. 



The Amoeba being thus permeated, as it were, with a 

 nutrient solution, the elements of the solution, hitherto 

 arranged in the form of peptones, mineral salts, and water, 

 become rearranged in such a way as to form new particles 

 of living protoplasm, which are deposited among the pre- 

 existing particles. In -a word, the food is assimilated, or 

 converted into the actual living substance of the Amoeba, 

 which must therefore grow, if nothing happens to counteract 

 this formation of new protoplasm. 



We have seen, however, that work results in a propor- 

 tional amount of waste (p. 66), and just as in the frog or in 

 ourselves, every movement of the Amoeba, however slight, 

 is accompanied by a proportional oxidation or low tempera- 

 ture combustion of the protoplasm, i.e. the constituents of the 



