II] OF THE BROWNIAN MOVEMENT 75 



progression as we ascend to higher and higher layers, so is it with 

 our particles within the narrow Umits of the little portion of fluid 

 under our microscope. 



It is only in regard to particles of the simplest form that these 

 phenomena have been theoretically investigated*, and we may take 

 it as certain that more complex particles, such as the twisted body 

 of a Spirillum, would shew other and still more comphcated mani- 

 festations. It is at least clear that, just as the early microscopists 

 in the days before Robert Brown never doubted but that these 

 phenomena were purely vital, so we also may still be apt to confuse, 

 in certain cases, the one phenomenon with the other. We cannot, 

 indeed, without the most careful scrutiny, decide whether the 

 movements of our minutest organisms are intrinsically "vital" (in 

 the sense of being beyond a physical mechanism, or working model) 

 or not. For example, Schaudinn has suggested that the undulating 

 movements of Spirochaete pallida must be due to the presence of a 

 minute, unseen, "undulating membrane"; and Doflein says of the 

 same species that "sie verharrt oft mit eigenthiimlich zitternden 

 Bewegungen zu einem Orte." Both movements, the trembling or 

 quivering movement described by Doflein, and the undulating or 

 rotating movement described by Schaudinn, are just such as may 

 be easily and naturally interpreted as part and parcel of the Brownian 

 phenomenon. 



While the Brownian movement may thus simulate in a deceptive 

 way the active movements of an organism, the reverse statement 

 also to a certain extent holds good. One sometimes Hes awake of 

 a summer's morning watching the flies as they dance under the 

 ceiling. It is a very remarkable dance. The dancers do not whirl or 

 gyrate, either in company or alone; but they advance and retire; 

 they seem to jostle and rebound; between the rebounds they dart 

 hither or thither in short straight snatches of hurried flight, and 

 turn again sharply in a new rebound at the end of each little rushf. 



* Cf. R. Gans, Wie fallen Stabe und Scheiben in einer reibenden Fliissigkeit? 

 Miinchener Bericht, 1911, p. 191; K. Przibram, Ueber die Brown'sche Bewegung 

 nicht kugelformiger Teilchen, Wiener Bericht, 1912, p. 2339; 1913, pp. 1895-1912. 



t As Clerk Maxwell put it to the British Association at Bradford in 1873, "We 

 cannot do better than observe a swarm of bees, where every individual bee is 

 flying furiously, first in one direction and then in another, while the swarm as 

 a whole is either at rest or sails slowly through the air." 



