FERMENTATION 285 



one, and by employing every imaginable infusion of wild 

 animals and tame; of flesh, fish, fowl, and viscera; of 

 vegetables of the most various kinds. If in all these 

 cases you find the dust infallibly producing its crop of 

 bacteria, while neither the dustless air nor the nutritive 

 infusion, nor both together, are ever able to produce this 

 crop, your conclusion is simply irresistible that the dust 

 of the air contains the germs of the crop which has ap- 

 peared in your infusions. I repeat there is no inference 

 of experimental science more certain than this one. In 

 the presence of such facts, to use the words of a paper 

 lately published in the "Philosophical Transactions," it 

 would be simply monstrous to affirm that these swarming 

 crops of bacteria are spontaneously generated. 



Is there then no experimental proof of spontaneous 

 generation? I answer without hesitation, none! But to 

 doubt the experimental proof of a fact, and to deny its 

 possibility, are two different things, though some writers 

 confuse matters by making them synonymous. In fact, 

 this doctrine of spontaneous generation, in one form or 

 another, falls in with the theoretic beliefs of some of the 

 ioremost workers of this age; but it is exactly these men 

 who have the penetration to see, and the honesty to ex- 

 pose, the weakness of the evidence adduced in its support. 



And here observe how these discoveries tally with the 

 common practices of life. Heat kills the bacteria, cold 

 numbs them. When my housekeeper has pheasants in 

 charge which she wishes to keep sweet, but which threaten 

 to give way, she partially cooks the birds, kills the infant 

 bacteria, and thus postpones the evil day. By boiling her 

 milk she also extends its period of sweetness. Some weeks 



