It can not be claimed for a moment that these changes by which the tobacco is cured and finally brought to a marketable condition are due wholly to bacteria.  There is no question that chemical and physical phenomena play an important part in them.  Nevertheless, from the moment when the tobacco is cut in the fields until the time it is ready for market the curing is very intimately associated with bacteria and fermentative organisms in general.  Some of these processes are wholly brought about by bacterial life; in others the micro-organisms aid the process, though they perhaps can not be regarded as the sole agents.

At the outset the tobacco producer has to contend with a number of micro-organisms which may produce diseases in his tobacco.  During the drying process, if the temperature or the amount of moisture or the access of air is not kept in a proper condition, various troubles arise and various diseases make their appearance, which either injure or ruin the value of the product.  These appear to be produced by micro-organisms of different sorts.  During the fermentation which follows the drying the producer has to contend with micro-organisms that are troublesome to him; for unless the phenomena are properly regulated the fermentation that occurs produces effects upon the tobacco which ruin its character.  From the time the tobacco is cut until the final stage in the curing the persons engaged in preparing it for market must be on a constant watch to prevent the growth within it of undesirable organisms.  The preparation of tobacco is for this reason a delicate operation, and one that will be very likely to fail unless the greatest care is taken.  In the several fermentative processes which occur in the preparation there is no question that micro-organisms aid the tobacco producer and manufacturer.  Bacteria produce the first fermentation that follows the drying, and it is these organisms too, in large measure, that give rise to all the subsequent fermentations, although seemingly in some cases purely chemical processes materially aid.  Now the special quality of the tobacco is in part dependent upon the peculiar type of fermentation which occurs in one or another of these fermenting actions.  It is the fermentation that gives rise to the peculiar flavour and to the aroma of the different grades of tobacco.  Inasmuch as the various flavours which characterize tobacco of different grades are developed, at least to a large extent, during the fermentation processes, it is a natural supposition that the different qualities of the tobacco, so far as concerns flavour, are due to the different types of fermentation.  The number of species of bacteria which are found upon the tobacco leaves in the various stages of its preparation is quite large, and from what we have already learned it is inevitable that the different kinds of bacteria will produce different results in the fermenting process.  It would seem natural, therefore, to assume that the different flavours of different grades may not unlikely be due to the fact that the tobacco in the different cases has been fermented under the influence of different kinds of bacteria.