40 PROBLEMS OF GENETICS 



is a vortex of chemical and molecular change." This description 

 gives much, if not all, that is of the essence of life. The living 

 thing is unlike ordinary matter in the fact that, through it, matter 

 is always passing. Matter is essential to it; but, provided 

 that the flow in and out is unimpeded, the life-process can go 

 on so far as we know indefinitely. Yet the living "vortex" 

 differs from all others in the fact that it can divide and throw 

 off other "vortices," through which again matter continually 

 swirls. 



We may perhaps take the parallel a stage further. A simple 

 vortex, like a smoke-ring, if projected in a suitable way will tw r ist 

 and form two rings. If each loop as it is formed could grow and 

 then twist again to form more loops, we should have a model 

 representing several of the essential features of living things. 



It is this power of spontaneous division which most sharply 

 distinguishes the living from the non-living. In the excellent 

 book dealing with the problems of development, lately published 

 by Mr. Jenkinson a special emphasis is very properly laid on the 

 distinction between the processes of division, and those of dif- 

 ferentiation. Too often in discussions of the developmental 

 processes the distinction is obscured. He regards differentiation 

 as the "central difficulty." "Growth and division of the nucleus 

 and the cells," he tells us, are side-issues. This view is quite 

 defensible, but I suspect that the division is the central difficulty, 

 and that if we could get a rationale of what is happening in 

 cell-division we should not be long before we had a clue to the 

 nature of differentiation. It may be self-deception, but I do 

 not feel it impossible to form some hypothesis as to the mode of 

 differentiation, but in no mood of freest speculation are we ever 

 able to form a guess as to the nature of the division. We see 

 differentiations occurring in the course of chemical action, in 

 some phenomena of vibration and so forth: but where do we 

 see anything like the spontaneous division of the living cell? 

 Excite a gold-leaf electroscope, and the leaves separate, but we 

 know that is because they were double before. In electrolysis 

 various substances separate out at the positive and negative 

 poles respectively. Now if in cell-division the two daughter- 



