THE IMMORTALITY OF THE PROTOZOA. 335 



manence of the dimensions and the forms of the living 

 organism. 



In a word, it is a rigorous law of living nature that 

 the cell can neither live indefinitely without growth, 

 nor grow indefinitely without division. 



Why is this so? Why is there this impossibility 

 of a regular regime in which the cell would be main- 

 tained in magnitude without diminution or increase? 

 Why has nutrition as a necessary consequence the 

 growth of the element? This is what we do not 

 positively know. 



Things are so. It is an irreducible fact, peculiar to 

 the protoplasm, a characteristic of the living matter 

 of the cell. It is the fundamental basis of the pro- 

 perty of generation. That is all we can say about it. 

 Real living beings have therefore inevitably an evolu- 

 tion. They are not unchangeable. In its simple form 

 this evolution consists in the fact that the cell grows, 

 divides, and diminishes by this division, begins the 

 upward march which ends in a new division. And 

 so on. 



Immortality of the Protozoa. It may happen, and 

 it does happen in fact, that this series of acts is 

 repeated indefinitely at any rate unless an accidental 

 cause should interrupt it The animal thus describes 

 an indefinite curve, constituted by a series of indenta- 

 tions, the highest point of which corresponds to the 

 maximum of size, and the lowest point to the 

 diminution which succeeds the division. This state of 

 things has no inevitable end if the medium does not 

 change. The being is immortal. 



In fact, the compound beings of a single cell, proto- 

 phytes and protozoa, the algae and the unicellular 

 mushrooms, at the minimum stage of differentiation, 



