SPONTANEOUS GENERATION. 305 



to the efifect that the failure of others to confirm his 

 results by no means upsets their evidence. To fix the 

 ideas, let us suppose that my colleague comes to the 

 laboratory of the Royal Institution, repeats there my 

 experiments, and obtains confirmatory results ; and 

 that he then goes to University or King's College, 

 •where, operating with the same infusions, he obtains 

 contradictory results. Will he be disposed to conclude 

 that the selfsame substance is barren in Albemarle 

 Street and fruitful in Gower Street or the Strand ? 

 His Alpine experience has already made known to him 

 the literally infinite dififej'ences existing between diffe- 

 rent samples of air as regards their capacity for putre- 

 factive infection. And, possessing this knowledge, will 

 he not substitute for the adventurous conclusion that 

 an organic infusion is barren at one place and sponta- 

 neously generative at another, the more rational and 

 obvious one that the atmospheres of the two localities 

 which have had access to the infusion are infective in 

 different degrees ? 



As regards workmanship, moreover, he will not fail 

 to bear in mind, that fruitfulness may be due to errors 

 of manipulation, while barrenness involves the pre- 

 sumption of correct experiment. It is only the careful 

 worker that can secure the latter, while it is open to 

 every novice to obtain the former. Barrenness is the 

 result at which the conscientious experimenter, whatever 

 his theoretic convictions may be, ought to aim, omit- 

 ting no pains to secure it, and resorting, only when 

 there is no escape from it, to the conclusion that the 

 life observed comes from no source which correct experi- 

 ment could neutralize or avoid. 



Let us again take a definite case. Supposing my 

 colleague to operate with the same apparent care on 

 100 infusions — or rather on 100 samples of the same 



