LIVING MATTER 



11 



they must take in food. If we watch patiently we 

 may see them eat. They do this in a primitive way. 

 They simply engulf another organism smaller than them- 

 selves. The parts of this organism which are unfit for 

 the building up of new protoplasm they eject from their 

 bodies. The nutritious material they retain and manu- 

 facture into protoplasm. This process is called assimi- 

 lation, 



Reproduction. — If we continue to watch, we may 

 notice that when one of these animals has attained its 

 full growth it splits into two small ones. (Fig. 4). 



Fie. 4.— Ameba dividing by fission. (From Sedgwick and Wilson, after Leidy.) 



Each of these assimilates food, grows to maturity and in 

 turn divides. The number of animals is thus rapidly 

 increased. This is the simplest form of reproduction. 



Universal Characteristics. — Irritability, assimila- 

 tion, and reproduction are universal characteristics of 

 living matter and of all organisms composed of it. The 

 study then of any organism means the study of the spe- 

 cific way in which these characteristics manifest them- 

 selves. 



Non-Living Matter in a Living Cell. — Suppose we 

 look at a cell which differs from those we have seen in 



