FERMENTATION. 559 
the sum of human knowledge regarding electricity, and 
for more than two thousand years fermentation was effected 
without any knowledge of its cause. In science one dis- 
covery grows out of another, and cannot appear without^ 
its proper antecedent. Thus, before fermentation could* 
be understood, the microscope had to be invented, and 
brought to a considerable degree of perfection. Note the 
growth of knowledge. Leeuwenhoek, in 1680, found yeast 
to be a mass of floating globules, but he had no notion 
that the globules were alive. This was proved in 1835 by 
Cagniard de la Tour and Schwann. Then came the ques- 
tion as to the origin of such microscopic organisms, and in 
this connection the memoir of Pasteur, published in the 
" Annales de Chimie" for 1863, is the inauguration of a 
new epoch. 
On that investigation all Pasteur's subsequent labors 
were based. Ravages had over and over again occurred 
among French wines. There was no guarantee that they 
would not become acid or bitter, particularly when 
exported. The commerce in wines was thus restricted, 
and disastrous losses were often inflicted on the wine- 
grower. Every one of these diseases was traced to the life 
of an organism. Pasteur ascertained the temperature 
which killed these ferments of disease, proving it to be so 
low as to be perfectly harmless to the wine. By the simple 
expedient of heating the wine to a temperature of fifty 
degrees Centigrade, he rendered it inalterable, and thus 
saved his country the loss of millions. He then went on 
to vinegar vinaigre, acid wine which he proved to be 
produced by a fermentation set up by a little fungus called 
Mycoderma aceti. Torula, in fact, converts the grape 
juice into alcohol, and Mycoderma aceti converts the 
alcohol into vinegar. Here also frequent failures occurred, 
and severe losses were sustained. Through the operation 
of unknown causes, the vinegar often became unfit for use, 
sometimes indeed falling into utter putridity. It had been 
long known that mere exposure to the air was sufficient to 
destroy it. Pasteur studied all these changes, traced them 
to their living causes, and showed that the permanent 
health of the vinegar was ensured by the destruction of 
this life. He passed from the diseases of vinegar to the 
study of a malady which a dozen years ago had all but 
ruiued the silk husbandry of France. This plague, which 
