IV] AND STRUCTURE OF THE CELL 325 



Cannon*. It depends on certain investigations of the Bjerknes, 

 father and sonf, which prove that bodies pulsating or oscillating J 

 in a fluid set up a field of force precisely comparable with the lines 

 of force in a magnetic field. Certain old and even familiar observa- 

 tions had pointed towards this phenomenon. Guyot had noticed 

 that bits of paper were attracted towards a vibrating tuning-fork; 

 and Schellbach found that a sounding-board so acts on bodies in its 

 neighbourhood as to attract those which are heavier and repel those 

 which are lighter than the surrounding medium; in air bits of 

 paper are attracted and a gas-flame is repelled. To explain these 

 simple observations, Bjerknes experimented with Httle drums 

 attached to an automatic bellows. He found that two bodies in 

 a fluid field, synchronously pulsating or synchronously oscillating, 

 repel one another when their oscillations are in the same phase, or 

 their pulsations are in opposite phase; and vice versa: while other 

 particles, floating passively in the same fluid, tend (as Schellbach 

 had observed before) to be attracted or repulsed according as they 

 are heavier or lighter than the fluid medium. The two bodies 

 behave towards one another like two electrified bodies, or like two 

 poles of a magnet; we are entitled to speak of them as "hydro- 

 dynamic poles," we might even call them " hydrodynamic magnets" ; 

 and pursuing the analogy, we may call the heavy bodies para- 

 magnetic, and the light ones diamagnetic with regard to them. 

 Lamb's hypothesis then, and Cannon's, is that the centrosomes act 

 as "hydrodynamic magnets." The explanation depends on oscilla- 

 tions which have never been seen, in centrosomes which are not 

 always to be discovered. But it brings together certain curious 

 analogies, and these, where we know so little, may be worth 

 reflecting on. 



If we assume that each centrosome is endowed with a vibratory 

 motion as it floats in the semi-fluid colloids, or hydrosols (to use 

 Graham's word) of the cell, we ma;^ take it that the visible intra- 

 cellular phenomena will be much the same as those we have 



* Op. cit. Cf. also Gertrud Woken, Zur Physik der Kernteilung, Z. f. allg, Physiol. 

 XVIII, pp. 39-57, 1918. 



t V. Bjerknes, Vorlesungen liber hydrodynamische Fernkrdjte, nach C. A. Bjerknes^ 

 Theorie, Leipzig, 1900. 



J A body is said to pulsate when it undergoes a rhythmic change of volume; 

 it oscillates when it undergoes a rhythmic change of place. 



