DIVISIONS INDUCED IN LYMPHOCYTES 



be seen at once a point on which we must lay stress 

 that the chromosomes are outside the nucleus 

 are formed by the conglomeration of the Altmann's 

 granules in the cytoplasm. As will be shown later 

 on, this is also the rule in leucocytes and some epithelial 

 cells as w r ell as in lymphocytes. 



The phenomenon of mitosis, then, as seen in these 

 cells when they are stained alive, differs very materially 

 from the usual descriptions of it as seen in cells which 

 have been killed, fixed, cut into sections or otherwise 

 manipulated, and stained. The old idea was although 

 divisions had not been seen actually in lymphocytes 

 that the chromosomes were formed out of some 

 chromatin which is within the nucleus, and that, inside 

 this again, a spindle, which does not exist in the rest- 

 ing stage, is formed. The nuclear wall was described 

 as vanishing during mitosis according to most con- 

 ceptions. But, as I have described, mitosis is a much 

 simpler phenomenon. 



The misconception has been due, I think, to several 

 factors. In the first place most cytological research has 

 been carried out with plant-cells, and animal cytology 

 has arisen from it. In the second place, cells up to now 

 have only been caught in the act of mitosis; their cycle 

 of cell-division has not been followed from the resting 

 stage to completed division in one individual cell. The 

 morphological elements of a resting cell have been 

 studied, and then those in one killed in the act of 

 division, and the part played by each element has been 

 deduced from its new position not watched through- 

 out. Lastly, owing to manipulation, the so-called 



