6 THE SCOPE OF THE NEW METHOD 



creatures which are amenable and can be excited or 

 made to divide almost at will. It is remarkable to 

 think that one can order samples of one's own or some 

 other person's white blood-corpuscles to reproduce 

 themselves at a given time, and that if they are properly 

 treated they will do so with obedient regularity. 

 Instead of the diagrammatic representations of karyo- 

 kinesis, from which every student learns his impressions 

 of cell-division, one is now able to appreciate mitosis 

 in its reality and to watch it through its various phases. 

 This is a very striking fact, but its interest grows when 

 we consider another very important lesson derived from 

 it, insomuch that, as will be seen later, there is strong 

 evidence that white corpuscles will multiply only in 

 response to a specific chemical agent. We now believe 

 that it is essential for a leucocyte to absorb an "aux- 

 etic" (<lv ^TI/COS, an exciter of reproduction) before it will 

 make any attempt to proliferate, and we have also 

 evidence that it is more than probable that other 

 human cells, and possibly all of them, proliferate in 

 response to a similar agency. It will be realized, there- 

 fore, that this method of study of the cell and of the 

 influences of chemical agencies upon it has opened 

 up a new field of work, not only in pathology, but in 

 physiology also. 



The proliferation of cells is the main theme of this 

 book. By this in-vitro method it has not only been learnt 

 that cells will divide in response to certain chemical 

 agents, but that these agents exist in the remains of 

 all dead tissues. Two of the substances which are 

 directly responsible for cell-reproduction within the 



