10 THE PHYSICAL BASIS OF LIFE 



the study of protoplasm and the cell may be destined to 

 pass more and more into the hands of the physiologist, the 

 physicist and the chemist ; and certainly the rising tide of 

 cell-research in these directions is of good augury for the 

 future experimental analysis of vital phenomena. There 

 are, however, other aspects of the problem which for the 

 present escape the precise cpiantitative methods of the 

 physicist and chemist, or are only beginning to come 

 within their range, but are none the less essential to our 

 view of the general problem. I refer to those phenomena 

 with which the cytologist, the geneticist and the embry- 

 ologist must try to deal ; and it is especially to the aspects 

 of the problem which these present that I here ask atten- 

 tion. 



The cytologist is first of all struck by the extraordinary 

 pains that nature seems to take to ensure the perpetua- 

 tion and accurate distribution of the components of the 

 system in cell-division, and hence in heredity. Nothing is 

 more impressive than the demonstration of this offered 

 by the nucleus of the cell ; but its obvious meaning is often 

 disregarded or treated with a blind scepticism which pre- 

 tends that no meaning exists. To our limited intelligence, 

 it would seem a simple task to divide a nucleus into equal 

 parts. The cell, manifestly, entertains a very different 

 opinion. Nothing could be more unlike our expectation 

 than the astonishing sight that is step by step unfolded to 

 our view by the actual performance. The nucleus is cut in 

 two in such a maimer that every portion of its net-like 

 inner structure is divided with exact equality between the 

 two daughter-nuclei, and the cell performs this spectacu- 

 lar feat with an air of complete and intelligent assurance. 

 The net-like framework is spun out into long threads or 

 chromosomes (Figs. 2, 3) ; these are divided lengthwise 

 into exactly similar halves; they shorten, thicken, sepa- 



