FERMENTS AND ARTIFICIAL FERMENTATIONS. 69 



History. The precise knowledge of the nature of 

 fermentation is of comparatively recent date. The 

 ancients, indeed, seem to have had an idea, however 

 vague, of this phenomenon, which was in their case 

 connected with the erroneous theory of spontaneous 

 generation. We all know the fable of the bees, born 

 from the putrefying body of a slain bull, which forms 

 one of the chief episodes of the Metamorphoses of 

 Ovid, and of the fourth book of Virgil's Georgics. 

 Aristotle says that, by means of heat, one living being 

 may have its birth in the corruption of another. . . . 

 Fermentation is, in fact, always accompanied by an 

 evolution of heat. The same idea was revived in the 

 Middle Ages, and during the Renaissance by alchemists 

 and physicians. Van Helmont, who lived early in 

 the seventeenth century, goes so far as to say, " It is 

 true that a ferment is sometimes so bold and enter- 

 prising as to form a living being. In this way, 

 lice, maggots, and bugs, our associates in misery, 

 have their birth, either within our bodies or in our 

 excrement. You need only close up a vessel full 

 of wheat with a dirty shirt, and you will see rats 

 engendered in it, the strange product of the smell 

 of wheat and of the animal ferment attached to the 

 shirt." 



Beside these singularly rash and purely fanciful 

 assertions, which show that imagination was allowed 

 in those days to play a much too important part 

 in natural science, we find a theory of the fermenta- 



