190 ESSAYS OF A BIOLOGIST 



We have only to look down a microscope to con- 

 vince ourselves of the alteration in our experience 

 that it would mean if we were to become sufficiently 

 diminished. The tiniest solid particles in fluids can 

 be seen to be in a continuous state of agitation — in- 

 explicable until it was pointed out that this mysterious 

 * Brownian ' movement was the inevitable result of 

 impacts by the faster-moving molecules of the fluid. 

 Many living things that we can still see are small 

 enough to live permanently in such agitation ; the 

 longest diameter of many bacteria is but half-a-micron 

 (a two-thousandth of a millimetre), and there are 

 many ultra-microscopic organisms which, owing to 

 their closer approximation to molecular dimensions, 

 must pass their lives in erratic excursions many times 

 more violent than any visible Brownian motion. 



If we could shrink, like Alice, at the persuasion of 

 some magic mushroom, the rain of particles on our 

 skin, now as unfelt as midges by a rhinoceros, 

 would at last begin to be perceptible. We should 

 find ourselves surrounded by an infinity of motes ; 

 titillated by a dance of sand-grains ; bruised by a rain 

 of marbles ; pounded by flights of fives-balls. What 

 is more, the smaller we became, the more individual- 

 ity and apparent free-will should we detect in the 

 surrounding particles. As we got still smaller, we 

 should, now and again, find the nearly uniform bom- 

 bardment replaced by a concerted attack on one 

 side or the other, and we should be hurled for perhaps 



