234 AMCEBA 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 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. 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 fats (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 animalcule 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 sub- 

 stance 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, how- 

 ever slight, is accompanied by a proportional oxidation 

 or low temperature combustion of the protoplasm, i.e., 

 the constituents of the protoplasm combine with oxygen, 



