CHAPTER II 



Amoeba as a typical organism The properties of protoplasm. 



IN illustration of the general principles dealt with in the fore- 

 going chapter we may now consider a definite concrete example 

 of a living organism. Probably none is better suited for this 

 purpose than the familiar Amoeba, which may be regarded as a 

 kind of pocket edition of a typical animal. 



Amoebae may be found creeping about on the mud at the 

 bottom of ponds and ditches. Although of microscopic size and, 

 usually at any rate, invisible to the naked eye, they are by no 

 means the smallest or simplest of living things, but exhibit 

 within the narrow limits of their gelatinous bodies a considerable 

 amount of structural differentiation. 



In general appearance (Fig. 2) an Amoeba resembles nothing 

 so much as an irregular speck of translucent jelly, but if we 

 watch it for a few minutes under the microscope we soon find 

 that it is something more than this. If in an active and 

 healthy condition it never maintains the same shape for long 

 together, but manifests an ever-changing irregularity as it 

 slowly creeps about from place to place, throwing out 

 irregular projections of its body first in one direction and 

 then in another and withdrawing old projections as new ones 

 are put forth. 



The viscid substance of which the entire body is composed is 

 protoplasm, but this protoplasm is not homogeneous throughout ; 

 on the contrary, it exhibits a characteristic differentiation into 

 parts or organs, which can be more or less readily distinguished 

 from one another and each of which has its own duties or 

 functions to perform. 



Inasmuch as it consists of but one protoplasmic unit, however, 

 we may speak of the body of an Amoeba as a single cell. 1 As 

 in all other typical cells, the most fundamental differentiation 



1 The origin and meaning of this term will be discussed more fully in a later 

 chapter. 



