236 AMGEBA CHAP. 



as metabolism constructive and destructive (p. 149). Living 

 protoplasm is thus the most unstable of substances ; it is 

 never precisely the same thing for two consecutive seconds ; 

 its existence, like that of a waterfall or a fountain, depends 

 upon the constant flow of matter into it and away from it. 



It follows from what has been said that if the income of 

 an Amoeba, i.e., the total weight of substances taken in (food 

 plus oxygen plus water), is greater than its expenditure or 

 the total weight of substances given out (faeces plus excreta 

 proper plus carbon dioxide), the animalcule will grow : if less 

 it will dwindle away : if the two are equal it will remain of 

 the same weight or in a state of physiological equilibrium. 



It is evident that Amoeba must also be able to perform 

 the function of reproduction. You have learnt that the cells 

 of the frog multiply \$y simple or binary fission (p. 106) : the 

 nucleus first divides into two, and then the surrounding 

 protoplasm ; and precisely the same thing occurs in Amoeba, 

 the reproduction of which therefore takes place by the 

 simplest method known, without any special repro- 

 ductive organs. The animalcule simply divides into two 

 Amoebae, each exactly like itself; and in doing so ceases to 

 exist as a distinct individual. Instead of the successive 

 production of offspring from an ultimately dying parent, we 

 have the simultaneous production of offspring by the division 

 of the parent, which does not die, but becomes simply 

 merged in its progeny. There can be no better instance of 

 the fact that reproduction is discontinuous growth. 



From this it seems than an Amoeba, unless suffering a 

 violent death, is practically " immortal," since it divides into 

 two completely organised individuals, each of which begins 

 life with half of the entire body of its parent, there being 

 therefore nothing left of the latter to die : it therefore 



