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 Unicellular Organisms 



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

 nospJicBrijim 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 

 Nussbaum in 1 884 in the case 

 of an infusorian, Oxytriclia. 

 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 Stejitor, another 

 infusorian, and with the same result (Fig. 159). 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 re'generation 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. — Styloiiychta, 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. 



