THE DIVIDING CELL 335 



they put forward against the theory have actually proved to be 

 additional supports thereto. 



Of course, abstract lines of force in a uniform medium are 

 necessarily invisible to the eye. The nearest approach to 

 rendering such visible is with transparent dielectrics in an 

 electrostatic field ; where, by the use of polarised light, we 

 can demonstrate that the medium is under strain along the 

 lines of force — and this is all that can be seen, even indirectly. 

 The only way to see the course of the lines is to render the 

 medium heterogeneous, and this must needs render the field 

 no longer uniform — a truism, which has been much ignored. 

 We do this for magnetic fields by the use of a small pivoted 

 needle, too small in relation to the size and strength of the field 

 to sensibly alter the direction and distribution of the lines : the 

 needle sets everywhere tangential to the direction of the line 

 that passes through its pivot. Another approximate mode is 

 the familiar one of shaking magnetic dust in air on "rough" 

 {i.e. not smooth frictionless) paper; the powder settles in lines 

 running approximately along lines of force. Faraday already 

 recognised that the presence of the dust altered the distribution 

 of the very lines of force which they were used to demonstrate ; 

 but bince in elementary physical text-books approximate state- 

 ments are frequently used without due caution, it is not aston- 

 ishing that biologists should have accepted such as complete, 

 and attempted to refute Gallardo's approximate statement by 

 applying the canons of lines of force to the visible mitosing 

 threads of the dividing cell. 



The need of using a heterogeneous mixture to model the 

 cell-field was felt very early indeed. In 1876 A. Giard, already 

 a brilliant young professor, keenly alive to the theoretical 

 possibilities of new discoveries, wrote in an abstract of the 

 then new facts of mitosis : 



L'explication physiologique du phenomene . . . doit etre 

 evidemment cherchee parmi les phenomenes physico-chimiques 

 et la production de poles electriques ou electro-magnetiques dans 

 le noyau. Peut-etre arrivera-t-on a mettre experimentalement 

 en evidence ces curieux processus en employant des spheres 

 liquides en suspension dans un autre liquide, comme le faisait 

 Plateau, mais en melangeant ces liquides de substances fortement 

 magnetiques et capables d'acquerir des poles sous l'influence 

 d'aimants puissants. II y aurait tout un ordre de recherches 

 a entreprendre dans ce sens {Bull. Sc. vol. vii. 1876, p. 258). 



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