SPONTANEOUS GENERATION. 307 



boiling for five minutes, or even less, would be sure to 

 destroy thena all ; in other localities the diffused germs 

 are so obstinate, that many hours' boiling would be 

 requisite to deprive them of their power of germina- 

 tion. The absence or presence of a truss of desiccated 

 hay would produce differences as great as those here 

 ■described. The greatest endurance that I have ever 

 observed — and I believe it is the greatest on record — 

 was a case of survival after eight hours' boiling. 



As regards their power of resisting heat, the in-^ 

 fusorial germs of our atmosphere might be classified 

 under the following and intermediate heads : — Killed in 

 five minutes ; not killed in five minutes but killed in 

 fifteen ; not killed in fifteen minutes but killed in 

 thirly.;, not killed in. thirty minutes but killed in an 

 hour ; not killed in an hour but killed in two hours ; 

 notliilled in two but killed in three hours; not killed 

 in three but killed in four hours. I have had several 

 •cases of survival after four and five hours' boiling, some 

 survivals after six, and one after eight hours' boiling. 

 Thus far has experiment actually reached ; but there is 

 no valid warrant for fixing upon even eight hours as 

 the extreme limit of vital resistance. Probably more 

 extended researches (though mine have been very exten- 

 sive) would reveal germs more obstinate still. It is 

 also certain that we might begin earlier, and find germs 

 which are destroyed by a temperature far below that of 

 boiling water. In the presence of such facts, to speak 

 of a death-point of bacteria and their germs would be 

 unmeaning — but of this more anon. 



' What present warrant,' it has been asked, ' is there 

 for supposing that a naked, or almost naked, speck of 

 protoplasm can withstand four, six, or eight hours' 

 boiling ? ' Eegarding naked specks of protoplasm I 

 make no assertion. I know nothing about them, save 



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