FERMENTATION AND DISEASE. 141 



just covered with warm water; you thus extract the juice of the beef 

 in a concentrated form. By properly boiling the liquid and filtering 

 it you can obtain from it a perfectly transparent beef-tea. Expose a 

 number of vessels containing this tea to the moteless air of your cham- 

 ber, and expose a number of similar vessels containing precisely the 

 same liquid to the dust-laden air. In three days every one of the lat- 

 ter stinks, and, examined with the microscope, every one of them is 

 found swarming with the bacteria of putrefaction. After three months, 

 or three years, the beef-tea within the chamber is found in every case 

 as sweet and clear, and as free from bacteria, as it was at the moment 

 when it was first put in. There is absolutely no difference between 

 the air within and that without, save that the one is dustless and the 

 other dust-laden. Clinch the experiment thus : Open the door of your 

 chamber and allow the dust to enter it. In three days afterward you 

 have every vessel within the chamber swarming with bacteria, and in a 

 state of active putrefaction. Here, also, the inference is quite as certain 

 as in the case of the powder sown in your garden. Multiply your proofs 

 by building fifty chambers instead of one, and by employing every im- 

 aginable infusion of wild animals and tame ; of flesh, fish, fowl, and vis- 

 cera ; 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 

 aide to produce this crop, your conclusion is simply irresistible that 

 the dust of the air contains the germs of the crop which, has appeared 

 in your infusions. I repeat, there is no inference of experimental sci- 

 ence more certain than this one. In the presence of such facts, to use 

 the words of a paper lately published in the " Philosophical Transac- 

 tions," 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 Avriters confuse matters by making them synonymous. 

 In fact, this doctrine of spontaneous generation, in one form or an- 

 other, falls in with the theoretic beliefs of some of the foremost work- 

 ers of this age ; but it is exactly these men who have the penetration 

 to see, and the honesty to expose, the weakness of the evidence ad- 

 duced 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 ago, 

 in the Alps, I made a few experiments on the influence of cold upon 



