54 CRYSTALS AND LIVING UNITS 



Thus the solution of this great problem passes beyond the reach 

 of actual observation. Microscopical evidence enables us to bring 

 it to this stage now, and it may perhaps never enable us to do 

 more. It reduces us to a consideration of two rival hypotheses, 

 and to a careful consideration of whatever evidence may be forth- 

 coming to influence us in our choice between these two possible 

 explanations. Nothing that can be said about the abundance of 

 recognisable atmospheric germs can directly affect the solution 

 of this problem. It is one which, if it has to do with germs at all, 

 has to do with invisible germs. But invisible germs can have only 

 a hypothetical existence, and even to this they can lay no claim, 

 unless observed phenomena cannot be explained without such 

 postulation. We must not forget the old^ and well-approved 

 logical rule — 



'Entia non sunt multiplicanda praeter necessitatem.' 



The ' law of parsimony ' may well be quoted for the benefit of 

 those who would ruthlessly people the atmosphere with countless 

 myriads of ' entities.' ' 



Let us now suppose however, for the sake of argument, that the 

 living units which may be seen to make their appearance in the 

 manner just described have, in reality, been formed de novo by a 

 process of synthesis from the organic molecules contained in the 

 infusion ; and further, from the point of view of this hypothesis, 

 let us consider what is known concerning the mutability of such 

 forms of life, and whether — as should be the case if they are in 

 fact new-born specks of living matter — they exhibit in an increased 

 degree a capacity for change in form and nature such as we have 

 found to be present in the case of crystalline matter. 



We may suppose that Bacteria of all kinds (including Bacilli, 



" Some of those who are so eager to demonstrate the prevalence of ' germs,' 

 are frequently carried away, by their enthusiasm, beyond the bounds of strict 

 logic. It suffices to show by the agency of the electric light or by some other 

 means, that air and water contain myriads of infinitesimally small particles, some 

 of which are organic in nature, in order that they may at once come to the 

 conclusion that the organic particles are 'germs.' But, seeing the countless 

 forms of life which exist upon the surface of the earth, and how these are from 

 moment to moment, during life as well as after death, undergoing a molecular 

 disintegration, it would be strange indeed if the atmosphere, and water which 

 has been exposed to it, did not contain multitudes of organic particles, both large 

 and small. The great majority of such mere organic particles, however, could 

 have no reasonable title to be called " germs." 



