SPONTANEOUS GENERATION. 597 



so obstinate that many hours' boiling would be requisite to deprive 

 them of their power of germination. 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 

 infusorial germs of our atmosphere might be classified under the fol- 

 lowing and intermediate heads : Killed in five minutes; not killed in 

 five minutes but killed in fifteen ; not killed in fifteen minutes but 

 killed in thirty ; not killed in thirty minutes but killed in an hour ; not 

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

 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 sur- 

 vivals 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. Prob- 

 ably 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 tem- 

 perature 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 

 mere nonsense but of this more anon. 



We have now to test one of the principal foundations of the doc- 

 trine of spontaneous generation as formulated in this country. With 

 this view, I place before my friend and co-inquirer two liquids which 

 have been kept for six months in one of our sealed chambers, exposed 

 to optically pure air. The one is a mineral solution containing in 

 proper proportions all the substances which enter into the composition 

 of bacteria, the other is an infusion of turnip it might be any one of 

 a hundred other infusions, animal or vegetable. Both liquids are as 

 clear as distilled water, and there is no trace of life in either of them. 

 They are, in fact, completely sterilized. A mutton-chop, over which 

 a little water has been poured to keep its juices from drying up, has 

 lain for three days upon a plate in our warm room. It smells offen- 

 sively. Placing a drop of the fetid mutton-juice under a microscope, 

 it is found swarming with the bacteria which live by putrefaction, 

 and without which no putrefaction can occur. With a speck of the 

 swarming liquid I inoculate the clear mineral solution and the clear 

 turnip-infusion, as a surgeon might inoculate an infant with vaccine 

 lymph. In four-and-twenty hours the transparent liquids have be- 

 come turbid throughout, and, instead of being barren as at first, they 

 are teeming with life. The experiment may be repeated a thousand 

 times with the same invariable result. To the naked eye the liquids 

 at the beginning were alike, being both equally transparent to the 

 naked eye they are alike at the end, being both equally muddy. In- 

 stead of putrid mutton-juice we might take as a source of infection 



