PHENOMENA OF MITOSIS 185 



unquestionably in the act of reproducing itself by / 

 mitosis. 



If any doubt existed as to whether the rod-shaped 

 bodies which had been seen in the cytoplasm of the 

 cells were really chromosomes, that doubt was now set 

 at rest. The cells were certainly not reproducing them- 

 selves when they were first placed on the jelly-film; 

 but after they had absorbed the contents of the jelly 

 during the eight-minutes' incubation at 37 C., they 

 gradually went through the process of cell-division by 

 mitosis, and on the removal of the slide from the 

 incubator they were found in the act of reproduction 

 with their chromosomes and centrosomes stained bright 

 scarlet. 1 



These mitotic divisions, induced for the first time 

 in living human cells, revealed the fact that the phe- 

 nomenon of mitosis in lymphocytes differed in many 

 details from the commonly accepted ideas regarding 

 karyokinesis which have been adopted from the study 

 (with the older fixation methods) of dead cells other 

 than lymphocytes. The nucleus does not vanish; it 

 forms the spindle. The chromosomes are not derived 

 from within the nucleus, but are formed from the 

 normal Altmann's granules which exist in the cyto- 

 plasm. The centrosomes are not mere "dots" at the 

 poles of the spindle, but are derived from the nucleolus 

 which has divided into two. 



Fresh films were made, and bloods taken from other 



1 That division had been seen in lymphocytes with this jelly, and some of 

 the facts which led up to this discovery were published by us in The British 

 MedicalJournal, October 23, 1909. 



