On the Heat necessary to kill Bacteria etc. 455 



to his work. This criticism, Spallanzani says*, " Without looldng 

 iuto details, couteuted itself by throwing doubt upon some of 

 the facts, and by explaining after its own fashion others whose 

 possibility it was willing to admit." He moreover warmly re- 

 probated the ignorant and disrespectful statements made by an 

 anonymous wTiter who had shown himself little worthy of being 

 heard upon the subjects in dispute. kSpallanzani on this occasion 

 very wisely said f: — "When it is a question concerning obser- 

 vations and experiments, it is necessary to have repeated them 

 with much circumspection before venturing to pronounce that 

 they are doubtful or untrustworthy. He who will allow him- 

 self to speak of them with contempt, and who can only attempt 

 to refute them with WTitiugs composed by the glimmer derived 

 from a treacherous lamp, will not find himself in a condition to 

 retain the esteem of learned men." The anonymous wTiter (in 

 his ' Lettres a un Americain ') to whom Spallanzani referred 

 had gone so far as to doubt the statements of Needham as to 

 the constant appearance of organisms in infusions which had 

 been previously boiled, and also intimated that even if they were 

 to be found, it was only because they had been enabled to resist 

 the destructive influence of the boUing fluid. This latter asser- 

 tion was emphatically denied by Spallanzani, his denial being 

 based upon a most extensive series of experiments with eggs in 

 great variety and with seeds of all degrees of hardness ; these 

 were all found to be killed by a very short contact with boiling 

 water. Spallanzani had thoroughly satisfied himself that even 

 very thick-coated seeds could not resist this destructive agent; 

 whilst he thought that the idea, entertained by some, of the eggs 

 of the lowest infusoria being protected from the injurious influ- 

 ence of the boiling w^ater by reason of their extreme minuteness, 

 was a supposition so improbable as scarcely to deserve serious con- 

 sideration. Such a notion was, he thought, wholly opposed to 

 what was known concerning the transmission of heat. AVhilst, 

 therefore, the opinion of those w^ho believe that eggs have the 

 power of resisting the destructive influence of boiling water could 

 be fully refuted, Spallanzani thought it by no means followed 

 that the infusoria which always, after a very short time, ap- 

 peared in boiling infusions had arisen independently of the ex- 

 istence of eggs. The infusions being freely exposed to the air, 

 it was very possible that this air had introduced eggs into the 

 fluids, which by their development had given birth to the infusoria J. 



After the lapse of a century it ha%at last been clearly shown 

 (hat this supposition of aerial contanuiJitiou advanced by Spallan- 

 zani (warrantable and natural as it was at the time) is one 



• Loc. cit. p. 9. t Loc. cit. p. 114. 



X A few pages further on this view is thus shortly expressed :— " II est 

 evident que toutes les tentatives faites avec le feu, peuvent bien servir a prouver 

 que les animaux mieroscopiques ne naissent point des ceufs que Ton supposait 

 exister dans les infusions avant qu'on leur fit scntir le feu ; mais ccla n'emp^che 

 pas qu'ils n'aient pu otre formtJs de ceiuc qui auront et^ portes dans les vaees 

 apres I'cbuUition." 



