PHYSIOLOGICAL RELATIONS OF NUCLEUS AND CYTOPLASM -^ ti 



We now turn to evidence which, though less direct than the above, 

 is scarcely less convincing. This evidence, which has been exhaus- 

 tively discussed by Hertwig, Weismann, and Strasburger, is drawn 

 from the history of the nucleus in mitosis, fertilization, and matura- 

 tion. It calls for only a brief review here, since the facts have been 

 fully described in earlier chapters. 



3. TJie Nucleus in Mitosis 



To Wilhelm Roux i^^i) we owe the first clear recognition of the 

 fact that the transformation of the chromatic substance during mitotic 

 division is manifestly designed to effect a precise division of all its 

 parts, — i.e. a panmeristic division as opposed to a mere mass-division, 

 — and their definite distribution to the daughter-cells. "The essential 

 operation of nuclear division is the division of the mother-granules " 

 {i.e. the individual chromatin-grains) ; "all the other phenomena are 

 for the purpose of transporting the daughter-granules derived from 

 the division of a mother-granule, one to the centre of one of the 

 daughter-cells, the other. to the centre of the other." In this respect 

 the nucleus stands in marked contrast to the cytoplasm, which under- 

 goes on the whole a mass-division, although certain of its elements, 

 such as the plastids and the centrosome, may separately divide, like 

 the elements of the nucleus. From this fact Roux argued, first, that 

 different regions of the nuclear substance must represent different 

 qualities, and second, that the apparatus of mitosis is designed to 

 distribute these qualities, according to a definite law, to the daughter- 

 cells. The particular form in which Roux and Weismann developed 

 this conception has now been generally rejected, and in any form it 

 has some serious difficulties in its way. We cannot assume a precise 

 localization of chromatin-elements in all parts of the nucleus ; for on 

 the one hand a large part of the chromatin may degenerate or be cast 

 out (as in the maturation of the ^ZZ), and on the other hand in the 

 Protozoa a small fragment of the nucleus is able to regenerate the 

 whole. Nevertheless, the essential fact remains, as Hertwig, Kolliker, 

 Strasburger, De Vries, and many others have insisted, that in mitotic 

 cell-division the chromatin of the mother-cell is distributed with the 

 most scrupulous equality to the nuclei of the daughter-cells, and that 

 in this regard there is a most remarkable contrast between nucleus 

 and cytoplasm. This holds true with such wonderful constancy 



dependent upon certain substances (oxydation ferments) that in some manner, not vet 

 clearly understood, facilitate the process; and the work of Spitzer ('97) has shown that 

 these substances (obtained from tissue-extracts) belong to the group of nucleo-proteids, 

 which are characteristic nuclear substances. The view thus suggested opens a further way 

 toward more exact inquiry into the nuclear functions, though it is not to be supposed that 

 the nucleus is the sole oxydative centre of the cell, as is obvious from the prolonged activity 

 of non-nucleaied protoplasmic masses. 



