THE EXTRACTS CONCENTRATED 271 



believed, after mature consideration, to be due to the 

 fact that we had not tried extracts in sufficient strength 

 for cells to respond to them under the detrimental 

 circumstances of the "experimental ten minutes." It 

 has already been pointed out as a corollary to these 

 circumstances that if a cell refuses to respond to a given 

 substance by not dividing in the experimental ten 

 minutes, it does not prove that that substance does 

 not actually contain an active principle for inducing 

 cell-division. We therefore considered the advisability 

 of concentrating the extracts, and then trying them 

 again by themselves. 



In the first instance this concentration process took 

 some little time. At this stage of our researches we 

 were unaware that the active augmenting principle 

 contained in the extracts was "thermostable" and 

 would resist boiling, and in consequence, at the outset, 

 we evaporated the extracts at the room tempera- 

 ture, which was a most tedious process. Moreover, 

 during this slow concentration of the extracts it was 

 necessary to test them from time to time to see if their 

 augmenting action was impaired at all with keeping. 



In the meantime other points were considered. It is 

 well known that cancer-cells frequently are seen to be 

 dividing with a reduced number of chromosomes. As 

 we have already stated, we believe that a reduction in 

 the number of chromosomes is due to increased pro- 

 lificity in cells; and this being the case, it seemed 

 probable that there might be some increase in or 

 augmentation of the cause of proliferation of the cells 

 of cancerous growths. Further, if this is the case, the 



