Page:Life and death (1911).djvu/179

 thread, and the filaments themselves (mitome) show very thick chromatic granulations, or microsomes, connected by the linin.

At the moment of reproduction of the cell these granulations blend into a stainable sheath which surrounds the filaments, and the latter dispose themselves so as to form a single thread. This chromatic filament, which has now become a single thread, is shortened as it thickens (spireme); it is then cut into segments, twelve or twenty-four in the case of animals and a larger number in the case of plants. These are chromosomes, or nuclear segments, or chromatic loops. Their part is a very important one. They are constant in number and permanent during the whole of the life of the cell. Let us add that the nucleus still contains accessory elements (nucleoli).

The Rôle of the Nucleus.—Experiment has shown that the nucleus presides over the nutrition, the growth, and the conservation of the cell. If, following the example of Balbiani, Gruber, Nussbaum, and W. Roux of Leipzig, we cut into two a cell without injuring the nucleus, the fragment which is denuded of the nucleus continues to perform its functions for some time in the ordinary manner, and in some measure in virtue of its former impulse. It then declines and dies. On the contrary, the fragment provided with the nucleus repairs its wound, is reconstituted and continues to live. Thus the nucleus takes a very remarkable part in the reproduction of the cell, but it is still a matter of uncertainty whether its rôle is here subordinated to that of the cellular body, or if it is pre-eminent. However that may be, it follows from this experiment that the nucleus presents all the characteristics of a vigorous vitality,