242 THE FLOATING-MATTEK OF TIIP: 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 ib, snaps asunder under the strain of 

 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 ? Let a quantity 



