342 



CELL-CHEMISTRY AND CELL-PHYSIOLOGY 



position, and movements of the nucleus in actively growing or metab- 

 olizing cells ; and from the history of the nucleus in mitotic cell- 

 division, in fertilization, and in maturation. 



I. Experiments on Unicelhilar Organisms 



Brandt ('77) long since observed that enucleated fragments of Acti- 

 nosphcerium soon die, while nucleated fragments heal their wounds 



and continue to live. The 

 first decisive comparison be- 

 tween nucleated and non-nu- 

 cleated masses of protoplasm 

 was, however, made by Moritz 

 Nussbaumin 1884 in the case 

 of an infusorian, Oxytricha. 

 If one of these animals be 

 cut into two pieces, the sub- 

 sequent behaviour of the two 

 fragments depends on the 

 presence or absence of the 

 nucleus or a nuclear frag- 

 ment. The nucleated frag- 

 ments quickly heal the wound, 

 regenerate the missing por- 

 tions, and thus produce a 

 perfect animal. On the other 

 hand, enucleated fragments, 

 consisting of cytoplasm only, 

 quickly perish. Nussbaum 

 therefore drew the conclusion 

 that the nucleus is indispens- 

 able for the formative energy 

 of the cell. The experiment 

 was soon after repeated by Gruber('85)in the case of Stentor, another 

 infusorian, and with the same result (Fig. 1 59). Fragments possess- 

 ing a large fragment of the nucleus completely regenerated within 

 twenty-four hours. If the nuclear fragment were smaller, the re- 

 generation proceeded more slowly. If no nuclear substance were 

 present, no regeneration took place, though the wound closed and 

 the fragment lived for a considerable time. The only exception 

 but it is a very significant one was the case of individuals in which 

 the process of normal fission had begun ; in these a non-nucleated 

 fragment in which the formation of a new peristome had already been 

 initiated healed the wound and completed the formation of the peri- 



Fig. 158. Sfylonyckia, and enucleated frag- 

 ments. [VERWORN.] 



At the left an entire animal, showing planes of 

 section. The middle piece, containing two nuclei, 

 regenerates a perfect animal. The enucleated pieces, 

 shown at the right, swim about for a time, but finally 

 perish. 



