98 BINUCLEATE CELLS IN TISSUE CULTURES. 



and of universal application, it may be possible to reconcile amitosis with the chro- 

 mosome hypothesis, for, since mitosis would be the only method of actual cell pro- 

 liferation, an unequal distribution of chromatin material to the daughter cells would 

 not be possible, according to our conception of the mitotic process. 



NUCLEAR FRAGMENTATION. 



A note may here be made regarding a curious form of nuclear division which 

 bears some resemblance to the one just described, but which differs from it in many 

 important particulars. It is known as nuclear fragmentation or uneciual multiple 

 nuclear fission, and was found to occur where the conditions for growth were not 

 favorable — for instance, in old cultures, in which the food and oxygen supply had 

 become depleted and katabolic products had accumulated (figs. 36 to 47) and in those 

 to which a toxic constituent had been added (e. g., ethyl alcohol, figs. 48 to 58). It 

 thus seems to be a pathological condition and is characterized by marked malfor- 

 mation of the nucleus, manifesting itself in lobulation and by a breaking away of 

 these lobules, so that what was formerly a single nucleus comes to consist of two, 

 three, or as many as seven or eight apparently separate pieces. 



The forms in which fragmentation presents itself are various, as may be seen 

 by reference to figures 36 to 47, drawn from a 6-da3^ growth from the stomach of a 

 5-day chick. The nucleus may be but moderately deformed, as in figure 49, where 

 a small bud has become constricted off, or there maj- be two, three, or more lobes or 

 appendages, as seen in figures 40 and 41. These small fragments are in all stages 

 of constriction, ranging from a blunt, sessile protuberance to a small pedunculated 

 mass, held sometimes by a mere thread, as in figure 46. Extremely irregular forms, 

 as 37, are not infrequent, and completely separated portions, as in 36, 42, and 45, 

 are quite often met with. Each fragment may or may not contain a nucleolus. 

 In the smallest pieces it is absent. In some cases, as in figure 45, if the nucleolus 

 happens to be caught in the constricting zone it may become separated, but this is 

 a rare occurrence. Where the nucleus is lobulated the number of lobules usually 

 exceeds the mmiber of nucleolar portions. The culture shows other evidences of 

 degeneration. The size of the nuclear portion seems here to bear no relationship 

 to the size of the karyosome fragment, as it does in the multiple direct division of 

 the nucleus described bj^ Schultz (1915). 



The extent to which this process of fragmentation may proceed is seen by 

 reference to the fact that 60 per cent of the nuclei were malformed in some way, and 

 34 per cent were actually fragmented, in ten fields from the preparation from which 

 figures 36 to 47 were drawn. There were no mitotic figures found m this preparation. 



In no case was there found any evidence of division of the cell protoplasm 

 following nuclear fragmentation; on the contrary, a sort of syncytium was formed, 

 in which the cytoplasm was filled with nuclear fragments of varying size. The 

 picture presented by such a nuclear complex is markedly different from that of the 

 giant cell, among the points of differentiation being the widely varying size of the 

 nuclei, their lobulation, and the presence of buds in process of separation from the 

 main nuclear mass. Again, in fragmentation the cytoplasm does not increase, 

 as in the case of the giant cell. 



