SPONTANEOUS GENERATION 885 



granted; but let me here recur to the remarks already 

 made in speaking of the experiments of Spallanzani, to 

 the effect that the failure of others to confirm his results 

 hy no means upsets their evidence. To fix the ideas, let 

 us suppose that my colleague comes to the laboratory of 

 the Eoyal 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 self- same substance is 

 barren in Albemarle Street and fruitful in Grower Street 

 or the Strand? His Alpine experience has already made 

 known to him the literally infinite differences existing 

 between different samples of air as regards their capacity 

 for putrefactive infection. And, possessing this knowl- 

 edge, will he not substitute for the adventurous conclusion 

 that an organic infusion is barren at one place and spon- 

 taneously 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 harrenness involves the presumption 

 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 convic- 

 tions may be, ought to aim, omitting 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 experiment could neutralize or avoid. 



