126 



General Biology 



some kind to form new particles and to add them to those already 

 existing. It is this ability to manufacture protoplasm from unorganized 

 matter that is one of the very fundamental properties of living matter. 



Any movement, or energy, expended by an animal is due to the 

 breaking down of complex molecules by what is known as oxidation. 1 

 The process of tearing down is called katabolism or dissimilation. This 

 is a slow combustion process giving out heat and producing energy by 

 which the animal can perform its various functions of life. The sub- 

 stance thus broken down and "used up" must also be accounted for in 

 any scientific study. This residual matter usually consists of solids and 

 fluids ; namely, water and some mineral substance, urea and carbon 

 dioxide (C0 2 ). Under this heading we include all secretions, excretions, 

 and products of respiration. 



Whenever glands produce a substance which is to be used again 

 by the animal, such product is called a secretion, while substances which 

 are thrown out of the body entirely, are called excretions. 



The contractile vacuole, since it probably contains uric acid, is con- 

 sidered an excretory organ, and because C0 2 also makes its way to the 

 exterior of the organ, it is supposed to be respiratory likewise. Amoeba, 



like any animal, grows more rapidly than 

 otherwise, if food is plentiful. Since food 

 is taken internally, the growth comes from 

 the center outward; in other words, by 

 intussusception. 



Whenever a cell reaches its full growth, 

 its outer shell, membrane, or whatever its 

 external covering may be called, not having 

 infinite possibilities in the way of extension 

 and stretching, usually breaks if more food 

 is taken. Cell division is the process by 

 which the plant or animal starts anew, thus 

 saving the parent cell from breaking. A 

 simple division into two (Fig. 47) is called 

 binary division. It will be remembered that 

 this mere splitting in two parts is the short- 

 est method by which cells divide, but, which, 

 as we have already said, probably does not 

 occur at all. It is, therefore, only because 

 our observational methods are not sufficiently delicate to note the 

 exact processes, that we speak of amitotic division at all. In Amoeba 

 proteus, however, which we are studying, there are two methods of 

 division : The so-called simple binary or amitotic, just mentioned, and 

 a process known as sporulation. A few instances have been reported 



Fig. 47. 



So-called amitotic division of 

 Amoeba, showing the changes which 

 take place during division. The 

 dark body in each figure is the nu- 

 cleus; the transparent circle, the 

 contractile vacuole; the outer, clear 

 portion of the body, the ectoplasm; 

 the granular portion, the endo- 

 plasm; the granular masses, food 

 vacuoles. Much magnified. 



1 Oxidation may be likened to a series of infinitesimal explosions which could be detected if we 

 had instruments delicate enough for such a purpose. 



