THE CURING OF TOBACCO 243 
allows the tobacco to undergo a second fermentation, called 
‘““sweating,’’ which brings the leaf into a better condition for use. 
The primary fermentation is clearly the essential process of 
tobacco-curing. During the fermentation some very essential 
changes in the tobacco take place. The chief of these changes are 
the following: A decrease in nicotin, an increase in alkaline reac- 
tion, an increase in ammonia, the disappearance of sugar, an in- 
crease in the amount of nitrate, a loss of water, a change in the 
texture of the leaf, a change in color (the final color brown) and a 
change in 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, concerning 
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 microérganisms are necessary to raise the 
temperature 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 I, II, III, 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 fermentation. If, however, they are inoculated with 
some of these bacteria, they will undergo a fermentation, al- 
though 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 
