II] OF MINUTE MAGNITUDES 71 



particle suffer an abrupt change here; what then can we attribute, 

 in the way of properties, to a corpuscle or organism as small or 

 smaller than, say, 0-05 or 0-03 /x? It must, in all probability, be a 

 homogeneous structureless body, composed of a very small number 

 of albumenoid or other molecules. Its vital properties and functions 

 must be extremely limited; its specific outward characters, even if 

 we could see it, must be nil; its osmotic pressure and exchanges 

 must be anomalous, and under molecular bombardment they may 

 be rudely disturbed; its properties can be Httle more than those of 

 an ion-laden corpuscle, enabling it to perform this or that specific 

 chemical reaction, to effect this or that disturbing influence, or 

 produce this or that pathogenic effect. Had it sensation, its ex- 

 periences would be strange indeed; for if it could feel, it would regard 

 a fall in temperature as a movement of the molecules around, and 

 if it could see it would be surrounded with light of many shifting 

 colours, like a room filled with rainbows. 



The dimensions of a cilium are of such an order that its substance 

 is mostly, if not all, under the pecuHar conditions of a surface-layer, 

 and surface-energy is bound to play a leading part in cihary action. 

 A cilium or flagellum is (as it seems to me) a portion of matter in 

 a state sui generis, with properties of its own, just as the film and the 

 jet have theirs. And just as Savart and Plateau have told us about 

 jets and films, so will the physicist some day explain the properties 

 of the cilium and flagellum. It is certain that we shall never 

 understand these remarkable structures so long as we magnify 

 them to another scale, and forget that new and pecuhar physical 

 properties are associated with the scale to which they belong*. 



As Clerk Maxwell put it, "molecular science sets us face to face 

 with physiological theories. It forbids the physiologist to imagine 

 that structural details of infinitely small dimensions (such as Leibniz 

 assumed, one within another, ad infinitum) can furnish an explana- 

 tion of the infinite variety which exists in the properties and functions 

 of the most minute organisms." And for this reason Maxwell 

 reprobates, with not undue severity, those advocates of pangenesis 



* The cilia on the gills of bivalve molluscs are of exceptional size, measuring 

 from say 20 to 120^ long. They are thin triangular plates, rather than filaments; 

 they are from 4 to lO/x broad at the base, but less than 1/x thick. Cf. D. Atkins. 

 Q.J. M.S., 1938, and other papers. 



