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 *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 régime in which the cell would be maintained 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 property of generation. That is all we can say about it. Real living beings have therefore inevitably an evolution. 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 indentations, 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, protophytes and protozoa, the algae and the unicellular mushrooms, at the minimum stage of differentiation,