FERMENTS AND ARTIFICIAL FERMENTATIONS. 69 
History—tThe 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 ofa 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- 
