DIVISION OF LYMPHOCYTES 21 



those substances which induced mitosis l in lympho- 

 cytes could also be made to cause the division 

 of polyinorphonuclear leucocytes and those epi- 

 thelial cells which were experimented on, but 

 in the present researches we have confined our 

 attentions entirely to the lymphocytes contained 

 in human blood from the peripheral circulation. 

 The reason for this is that, as already pointed 

 out (1), it is much easier to induce lymphocytes 

 to divide (under the experimental conditions) 

 than the other cells, owing to the fact that they 

 are less fragile and seem to have a higher vitality. 

 At the same time it may be mentioned that, 

 during the experimentation with the different 

 substances to be enumerated, divisions have also 

 been occasionally induced in polymorphonuclear 

 leucocytes. Moreover, as already noted, the only 

 substances with which mitosis has been induced 

 in epithelial cells are those which also have the 

 auxetic action on lymphocytes and leucocytes. 



In these researches the technique employed has 

 been the in-vitro method described in former 

 papers ; that is to say, the cells are spread on 

 the surface of a film of agar jelly set on a slide 

 and examined microscopically. The jelly contains 



1 The application of the term mitotic to these induced figures has 

 been questioned, because it has been suggested that, since there is 

 no newly formed spindle and since the cytoplasmic granules form 

 the chromosomes, the divisions should be considered to be of the 

 amitotic variety. But we wish to maintain our original contention, 

 for, though many atypical figures occur, divisions have been induced 

 in lymphocytes in which the cells have gone through the phases 

 similar to those of karyokinesis, and, with experience, it will be seen 

 that the so-called atypical figures are in reality phases of the 

 same phenomenon, except that the cells are distorted. The nucleus 

 forms the spindle, however, and the granules form the chromosomes. 

 2* 



