It must not, however, be inferred that the differences in grades of tobacco grown in different parts of the world are due solely to variations in the curing processes and to the types of fermentation.  There are differences in the texture of the leaves, differences in the chemical composition of the tobaccoes, which are due undoubtedly to the soils and the climatic conditions in which they grow, and these, of course, will never be affected by changing the character of the ferment active processes.  It is, however, probable that in so far as the flavours that distinguish the high and low grades of tobacco are due to the character of the fermentative processes, they may be in the future, at least to a large extent, controlled by the use of pure cultures in curing processes.  Seemingly, then, there is as great a future in the development of this fermentative industry as there has been in the past in the development of the fermentative industry associated with brewing and vinting.

Opium.

Opium for smoking purposes is commonly allowed to undergo a curing process which lasts several months.  This appears to be somewhat similar to the curing of tobacco.  Apparently it is a fermentation due to the growth of microorganisms.  The organisms in question are not, however, bacteria in this case, but a species of allied fungus.  The plant is a mould, and it is claimed that inoculation of the opium with cultures of this mould hastens the curing.

Troublesome fermentations.

Before leaving this branch of the subject it is necessary to notice some of the troublesome fermentations which are ever interfering with our industries, requiring special methods, or, indeed, sometimes developing special industries to meet them.  As agents of decomposition, bacteria will of course be a trouble whenever they get into material which it is desired to preserve.  Since they are abundant everywhere, it is necessary to count upon their attacking with certainty any fermentable substance which is exposed to air and water.  Hence they are frequently the cause of much trouble.  In the fermentative industries they occasionally cause an improper sort of fermentation to occur unless care is taken to prevent undesired species of bacteria from being present.  In vinegar making, improper species of bacteria obtaining access to the solution give rise to undesirable flavours, greatly injuring the product.  In tobacco curing it is very common for the wrong species of bacteria to gain access to the tobacco at some stage of the curing and by their growth give rise to various troubles.  It is the ubiquitous presence of bacteria which makes it impossible to preserve fruits, meats, or vegetables for any length of time without special methods.  This fact in itself has caused the development of one of our most important industries.  Canning meats or fruits consists in nothing more than bringing them into a condition in which they will be preserved