SPONTANEOUS GENERATION 337 



germinated after four hours' boiling. The germs of the 

 air vary as much among themselves as the seeds of the 

 botanist. In some localities the diffused germs are so ten- 

 der that boiling for five minutes, or even less, would be 

 sure to destroy them all; in other localities the diffused 

 germs are 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 de- 

 scribed. The greatest endurance that I have ever ob- 

 served 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 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 extensive) 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 be- 

 low 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, 

 SCIENCE VI 15 



