242 THE FLOATING-MATTER OF THE AIR. 



twilight of antiquity, and in this our day there is no 

 more proof of the spontaneous generation of the one 

 than there is of the spontaneous generation of the 

 other. 



I stated a moment ago that the fermentation of 

 grape-juice was spontaneous ; but I was careful to add, 

 ' in what sense spontaneous will appear more clearly 

 by-and-by.' Now this is the sense meant. The wine- 

 maker does not, like the brewer and distiller, delibe- 

 rately introduce either yeast, or any equivalent of yeast, 

 into his vats ; he does not consciously sow in them any 

 plant, or the germ of any plant ; indeed, he has been 

 hitherto in ignorance whether plants or germs of any 

 kind have had anything to do with his operations. 

 Still, when the fermented grape-juice is examined, the 

 living Torula concerned in alcoholic fermentation 

 never fails to make its appearance. How is this ? If 

 no living germ has been introduced into the wine-vat, 

 whence comes the life so invariably developed there ? 



You may be disposed to reply, with Turpin and 

 others, that in virtue of its own inherent powers, the 

 grape-juice when brought into contact with the vivi- 

 fying atmospheric oxygen, runs spontaneously and of 

 its own accord into these low forms of life. I have not 

 the slightest objection to this explanation, provided 

 proper evidence can be adduced in support of it. But 

 the evidence adduced in its favour, as far as I am ac- 

 quainted with it, snaps asunder under the strain ol 

 scientific criticism. It is, as far as I can see, the evi- 

 dence of men who, however keen and clever as ob- 

 servers, are not rigidly trained experimenters. These 

 alone are aware of the precautions necessary in investi- 

 gations of this delicate kind. In reference, then, to the 

 life of the wine- vat, what is the decision of experiment 

 when carried out by competent men ? Lot a quantity 



