18 THE GERM THEORY OF DISEASE. 



be untrue. Very many denied the relevance of the facts 

 brought forward, and sought other explanations; but without 

 gaining much favor. Earnest men were examining the act 

 of fermentation ; and especially seeking the causes of putrefac- 

 tion. Why should a dead body pass so quickly into a state 

 of putrefaction? Enough was known to convince many 

 thoughtful men that putrefaction was not caused by anything 

 inherent in the flesh itself; for, under some circumstances, 

 decomposition did not take place. They had learned to pre- 

 vent it, at least for a long time, in meats that were preserved 

 for food. Many other circumstances came up which furnished 

 food for thought, and which shook the faith in the idea that 

 fermentation of vegetable substances and putrefaction of 

 animal tissues were truly spontaneous and inherent in the 

 nature of such bodies. 



EARLY DISCOVERIES. 



In the first decade of the sixteenth century, Von Helmont 

 had shown that the gas arising from fermentation was different 

 from common air ; was carbon dioxide. And the other pro- 

 duct, alcohol, had been known from the earliest historic times, 

 but it was not isolated until the fifteenth century, though its 

 distillation was regularly practiced in the eighth. It had been 

 shown by Gay-Lussac, that grape juice does not ferment in 

 vacuo. This was discovered in a now classical series of 

 experiments, in which this experimenter caused clean grapes 

 to ascend through the mercury of a large barometer into the 

 Toricellian vacuum, and then crushed them by means of a mer- 

 curial column. This juice remained unchanged, but the addi- 

 tion of small quantities of air set up fermentation. Stahl, in 

 1731, arrived at the conclusion that fermentation and putre- 

 faction were similar or identical processes. This was also the 

 opinion of Justus Liebig, one hundred years later. 



