226 ALCOHOL, VINEGAR, SAUER KRAUT, TOBACCO, SILAGE, FLAX. 
flavor. These numerous changes, while quite varied in nature, are 
mainly due to oxidation. 
The Cause of Tobacco Fermentation. Three different 
theories have been held and, to a certain extent, are still held, con- 
cerning the cause of the fermentation. While not one of them 
explains all the facts, all three may, in a measure, be correct. 
The Chemical Theory. This assumes that the free oxygen of 
the air acts directly upon the cells of the tobacco leaves, although it 
is admitted that microorganisms are necessary to raise the tem- 
perature sufficiently to make the oxidation possible. 
The Bacterial Theory. This assumes that the fermentation is 
the result of bacterial growth. Bacteria are found upon the leaves 
of fermenting tobacco, and several distinct species have been 
isolated and carefully studied. Some of them are well-known 
species, but others are peculiar to tobacco. Some have been 
named B. tobacci /, //, ///, IV, and V. It has been claimed that 
these have a causal relation to the fermentation of the tobacco, and 
experiments have been carried out to test it. Tobacco leaves have 
been sterilized and it is found that they will not undergo fermenta- 
tion. If, however, they are inoculated with some of these bacteria, 
they will undergo a fermentation, although the result does not show a 
good flavor or aroma, which fact suggests that, though bacteria are 
concerned in the process, there are other factors. 
The Enzyme Theory. The recognized importance of enzymes 
in fermentation in general, has naturally raised the question of 
their relation to tobacco-curing. Enzymes are known to be pro- 
duced by plants, and would be expected in the tobacco leaves. 
Indeed, they are found there readily enough, and among them are 
certain enzymes called ozydases, peroxydases, and catalases, which 
have the power, under different conditions, of producing an oxida- 
tion of other substances. Are not these, rather than bacteria, the 
cause of tobacco fermentation, which is chemically an oxidation? 
Arguments for this view are found in the following facts: 
i. The extremely rapid rise in temperature is too high to be 
accounted for by ordinary bacterial action. Fermentation due to 
bacteria may certainly produce a rise in temperature, but a rise as 
