150 THE UNIQUENESS OF LIFE 



gering, namely, cell-division. After extraordinarily intricate 

 and uniform internal movements of particles a cell divides 

 with meticulous accuracy into two precisely similar halves, 

 sometimes, strange to say, into two quite dissimilar halves. 

 As we have already remarked, it is one of the wonders of 

 the world. Like not a few others, Professor Hartog has been 

 studying the dividing cell for many years, and he believes 

 that he has discovered a new force operative in the process. 

 He is quite clear that well-known physical forces are at play 

 in the dividing cell, such as mechanical tensions, surface 

 tensions, and osmotic actions; he is also clear that agencies 

 are at work which occur elsewhere in living organisms, but 

 whose physical interpretation is uncertain, such as protoplas- 

 mic streaming; yet when he has made allowance for all 

 these he finds evidence of the working of a new force which 

 he calls " mitokinetism ". He does not know the proximate 

 cause of this force or its relation to other forces, he knows 

 it by its works, and he cannot identify it with any other 

 force, electrostatic for instance. Nor does he base his own 

 vitalistic belief on his " mitokinetism ". We have here the 

 basis of a theory that organisms have a monopoly of some 

 peculiar energy or energies, and are therefore apart both 

 from machines and from not-living things in general. 



A clear statement of this position was given by the late 

 Prof. Richard Assheton-, who suggested that instead of being 

 satisfied with the more or less mystical Entelechy we should 

 look out for some form of energy peculiar to living matter. 

 In 1894, Roux observed that if the cleavage-cells of the ovum 

 of the frog (Rana fusca) towards the end of segmentation 

 be isolated and floated in a suitable medium, they show 

 mutual attraction. The sides of one cell become drawn out 

 towards a neighbouring cell ; the cells move towards one 



