20 
Transactions Texas Academy of Science. — 1907. 
Prior to the time of Lavoisier and his epoch-making work so little 
was known of chemistry that this subject did not to any considerable 
extent, enter into the speculations of the time regarding fermentation; 
the external features of the process excited more interest than did the 
internal causes of the phenomena. Stahl, the author of the Phlogistin 
theory, impressed by the marked disturbance of particles in fermenting 
fluids, and by the evolution and escape of gas during fermentation, 
conceived a theory of action in which fermenting particles were assumed 
to have an internal motion which they transmit to quiescent bodies in 
contact, and by this means cause them also to undergo' fermentation. 
This theory was generally accepted and dominated public thought on 
this subject until, many years later, it was displaced by the chemical 
theory of Lavoisier. This distinguished chemist, impressed with the 
chemical features of the process and apparently oblivious to its ferment 
features, claimed that alcoholic fermentation consisted in a chemical 
conversion of sugar into alcohol and carbon dioxide; the means by 
which the conversion was brought about was entirely ignored. Of 
course, Lavoisier knew that sugar could not ferment itself into alcohol 
and carbon dioxide, and that an outside force was needed to induce the 
chemical change; but this subject did not receive his attention, and it 
was not until some lime later that the subject of an outside force was 
taken up by Gay Lussac, a pupil of Lavoisier, who theorized that this 
force is oxygen. 
As time passed the field of observation in this department of science 
became greatly enlarged; improvements in the microscope and in micro- 
scopic lens greatly increased the magnifying power of the instrument, 
and led to the discovery that alcoholic fermentation is constantly asso- 
ciated with the presence of microscopic cells, later shown to be yeast 
cells. Besides, the field was enlarged by the discovery of other kinds 
of fermentation than the alcoholic, and of other ferments than yeast 
cells; the existence of non-living ferments (enzymes) was discovered 
during this period. 
The important work that Schwann, Hoffman, and others accom- 
plished should be noticed in this connection. Having first determined 
that an infusion of meat, sterilized by heat and hermetically sealed, 
would not decompose, but that decomposition did occur when ordinary 
air was permitted access, Schwann arranged his apparatus so that air 
could enter the flask containing the sterile meat infusion, but in doing 
this must pass through a glass tube heated to whiteness so that all living 
substances the entering air contained would be killed. He found when 
these precautions were taken that the free entrance of air did not cause 
the meat infusion to decompose, and he concluded therefrom, first, that 
oxygen does not supply the force (as claimed by Gay Lussac) that 
