EXPERIMENTAL TEN MINUTES 251 



At present there is nothing for it but to induce 

 divisions with the cells spread out on jelly under a 

 cover-glass; and it must be remembered throughout 

 that these conditions are most detrimental to the cells. 

 Pressed in this way into the jelly by means of a cover- 

 glass, which to living cells must be proportionately of 

 enormous weight, leucocytes and lymphocytes will not 

 live more than about three-quarters of an hour. Al- 

 though they w r ill exist for this time, and although 

 amoeboid movements may be excited in them during 

 greater part of it, it is obvious that the cells are in 

 reality dying slowly all the time. Since the ease with 

 which one can induce divisions in lymphocytes varies 

 directly with the vitality of the cells, it is clear that 

 w r hatever is done to induce mitosis must be done 

 quickly, and by practical experiment it has been found 

 best to observe the general rule that, when one attempts 

 to induce cells to divide on the microscope slide one 

 must so arrange the jelly-film that the cells will be in 

 the act of mitosis within ten minutes. This is a serious 

 disadvantage appertaining to in-vitro experimentation, 

 which cannot so far be overcome, and it is important 

 to remember it throughout. The cells are labouring 

 under abnormal difficulties which modify one's deduc- 

 tions from the facts seen ; and since this important point 

 will frequently have to be considered, it is convenient 

 to standardise these detrimental conditions and desig- 

 nate them the "experimental ten minutes." 



Two corollaries depend on the "experimental ten 

 minutes." Since the induction of a division in a cell 

 depends on the diffusion into it of a certain quantity of 



