SCIENTIFIC USE OF THE IMAGINATION. 125 



and bacteria of the microscopic field are as behemoth 

 and leviathan. The law of relativity may to some ex- 

 tent explain the different attitudes of two such persons 

 with regard to the question of spontaneous generation. 

 An amount of evidence which satisfies the one entirely 

 fails to satisfy the other; and while to the one the last 

 bold defence and startling expansion of the doctrine 

 by Dr. Bastian will appear -perfectly conclusive, to the 

 other it will present itself as merely imposing a labour 

 of demolition on subsequent investigators.* 



Let me say here that many of our physiological 

 observers appear to form a very inadequate estimate of 

 the distance which separates the microscopic from the 

 molecular limit, and that, as a consequence, they some- 

 times employ a phraseology calculated to mislead. 

 When, for example, the contents of a cell are de- 

 scribed as perfectly homogeneous or as absolutely 

 structureless, because the microscope fails to discover 

 any structure; or when two structures are pronounced 

 to be without difference, because the microscope can dis- 

 cover none, then, I think the microscope begins to play 

 a mischievous part. A little consideration will make it 

 plain that the microscope can have no voice in the 

 question of germ structure. Distilled water is more 

 perfectly homogeneous than any possible organic germ. 

 What is it that causes the liquid to cease contracting at 

 39 Fahr., and to expand until it freezes? We have 

 here a structural process of which the microscope can 

 take no note, nor is it likely to do so by any conceivable 

 extension of its powers. Place distilled water in the 

 field of an electro-magnet, and bring a microscope to 

 bear upon it. Will any change be observed when the 

 magnet is excited? Absolutely none; and still pro- 



* When these words were uttered I did not imagine that the 

 chief labour of demolition would fall upon myself. 1878. 



