INFLUENCE OF VITALITY 231 



slowly. Twenty minutes afterwards, when all the 

 chromatin was stained, it was seen that the mitosis 

 had been arrested in those early stages reached at the 

 seventh minute. 



Thus it appears from this experimentation that not 

 only will a lymphocyte not reproduce itself in vitro 

 unless it absorbs a chemical "exciter of reproduction," 

 but also the actual stage reached in its act of mitosis 

 varies directly with the quantity of that substance 

 which has diffused into the cell. It follows that, 

 in vitro, before a cell will reproduce itself completely 

 it must receive a definite quantity or dose of the 

 chemical substance. 



In addition to the above factors, the divisions of the 

 cells depend upon their vitality. If some blood is 

 citrated and kept for two days, it is very difficult to 

 induce divisions in the lymphocytes. The longer cells 

 have been shed the slower they are to respond to the 

 division-inducing action of the stain, in spite of the fact 

 that their coefficient of diffusion has fallen. It is im- 

 possible to induce divisions in cells with auxetic jelly if 

 other cells from the same sample of blood will not show 

 excited movements on kinetic jelly. 



The foregoing points showed that the reproduction 

 of lymphocytes in vitro depended entirely on the 

 aniline dye. The dye did not merely increase the cells' 

 propensity to divide; it actually caused the division. 

 Lymphocytes had never been seen to divide before, and 

 they certainly will not divide in vitro unless one takes 

 deliberate steps to make them do so. Mitosis is a 

 complex phenomenon which only occurs as an act of 



