ence one discovery 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 question as to the origin of such microscopic organisms,
and in this connection '`the memoir of Pasteur, published in the
'Annales de Chimie' for 1862, is the inauguration of a new epoch.

On that investigation all Pasteur's subsequent labours were based.
Ravages had over and over again occurred among French wines. There
was no guarantee that they ould not become acid or bitter, particularly
when exported. The commerce in wines was thus restricted, and disastrous
losses were ften 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--vin aigre, 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 ruined the silk husbandry of France. This
plague, which received the name of _pebrine_, was the product of a
parasite which first took possession of the intestinal canal of the
silkworm, spread throughout its body, and filled the sack which ought
to contain the viscid matter of the silk. Thus smi