76 THE ACTIVE FORCES OF LIVING ORGANISMS 



regarded as the probable course of events in an 

 ordinary electrical cell that there should be the less 

 hesitation in accepting it as representing the truth, at 

 least in its main lines. 

 Absorp- In order to study the processes of nutrition in their 



tion in the . . , i • i • • 



amoeba. Simplest form it IS necessary to begin by examining 

 them, so far as that is possible, in some unicellular 

 organism such as the amoeba. We may imagine such 

 a one to have encountered some little edible particle, 

 and to be in the act of absorbing it. The granular 

 protoplasm of the amcsba separates to allow it to 

 enter, pseudopodia are stretched out on either side ; 

 the body of the amoeba then closes on the edible 

 particle, which is thus held within it until much of 

 the nutriment is withdrawn. By what forces is this 

 brought about ? What prompts the amoeba to seize 

 upon its food ? Evidently there can be no question 

 of chance impact. The particle is not driven into the" 

 amoeba by a stray current, for any force of this kind 

 would probably act on both alike. Moreover, if the 

 particle were not edible the amoeba would not stretch 

 forth its pseudopodia, nor would its granular substance 

 divide so as to receive it. But in order that a 

 particle may be edible two things are necessary : it 

 must be soluble and must be capable of undergoing 

 oxidation ; a particle answering to these requirements 

 would show a marked tendency to enter into chemical 

 action, and as soon as it collided with the more highly 

 oxygenated substance of the amoeba, a state of things 

 decidedly favourable to development in this direction 



