Multiplication and Migration of Nucleoli in Nerve Cells of Mammals 205 



into the cyptoplasm of the cell ^ seemed to indicate the destiny of these 

 bodies, which are apparently continuously produced in the nerve cells of 

 the animals here investigated, and a particular study of this phenomenon 

 was therefore made. It has been claimed that the alleged migration of the 

 nucleoli is due to some mechanical force such as the dragging or pressing 

 of the edge of the microtome knife in the process of cutting sections, or to 

 the action of gravity.- 



In the present observations nucleoli partly extruded through the nuclear 

 membrane and in the cytoplasm clear of the nucleus were frequently found. 

 In the great majority of these cases the apparent extrusion of the nucleolus 

 was undoubtedly due to the action of the knife. Such nucleoli were always 

 in an exactly similar position in relation to the nucleus and cytoplasm in 

 every section in a series. Thus, if one were found half-way through or 

 outside the nuclear membrane to the lower right-hand side of the centre 

 of the nucleus, the other nucleoli would be displaced in exactly the same 

 direction in other cells, not only in the same section, but in the other 

 sections of the series. Furthermore, the nucleolus thus displaced carried 

 with it a considerable amount of liniu with its contained chromatin gran- 

 ules, and a large empty space in the nucleus with the broken ends of the 

 strands of linin round it could be found in all these cases (fig. 10). Also 

 the nuclear membrane was always definitely ruptured, and there was never 

 any sign of its being reconstructed, which one would expect to find, and, 

 as will be seen, actually was found, when the nucleoli were extruded 

 normally ; for nuclei, even when they contain several nucleoli, are usually 

 found to possess a membrane without any large ruptures, and fresh 

 nucleoli are apparently constantly being produced. An interesting fact 

 is, however, indicated by this occurrence. The nucleoli must be of a highly 

 dense and resistent structure as compared with the rest of the cell, as the 

 edge of the knife, when it happens to catch one of them, does not cut 

 through it as it does through the other cellular constituents, but carries it 

 bodily along for a considerable distance. 



In a, comparatively speaking, few cells, however, a true migration of 

 the nucleolus was observed, and the phenomenon is here described in 

 some detail, as it appears to differ in some respects from what has been 

 stated to occur by other authors : some points seem to have escaped notice 

 altogether. 



The staining reaction of the nucleoli when inside the nucleus was very 

 marked with certain combinations used in the present investigation. Thus 

 with Method A the nucleolus stains blue or violet, while with Method B 

 it stains brilliant scarlet. 



The way in which the passage of the nucleolus from the nucleus occurs 

 is apparently as follows : — A nucleolus lies for some time against the 



^ Montgomery, Rhode, Hatai, and others. 



^ Herrick, " Movi'inents of the Nncleolns through the Action of Gravity," Anatoni. 

 Anz., Bd. X. 95. 



