There are many industrial processes which are more or less dependent for success on bacterial fermentations. The subject is young, but the results already obtained are seen to be of immense importance from a scientific point of view, and to open up vistas of practical application already being taken advantage of in commerce, while problems are continually being raised by the forester, the agriculturist, the gardener, the dairyman, the brewer, dyer, tanner, and with regard to various industries, which will eventually confer great advantages in their economic application. The remarkable discovery made by Alvarez of the bacillus, which converts a sterilised decoction of the indigo plant into indigo sugar and indigo white, the latter then oxidising to form the valuable blue dye, whereas the sterile decoction itself, even in presence of oxygen, forms no indigo, plainly proves how these minute organisms may be turned to a good account. There are, however, important points to be determined as to the action of the fermentation brought about by these enzymes, and the appearance of certain mysterious diseases in the indigo vats. Again, certain stages in the preparation of tea and tobacco leaves are found to depend upon very carefully regulated fermentations, which must be stopped at the right moment, or the product will be spoilt. Regarding the possible _rôle_ of bacteria, the West Indian tobacco has a special bacterium, which has been isolated and found to play a very important part in its flavour. Every botanist knows that flax and hemp are the best fibres of Linum and Cannabis respectively, separated by steeping in water until the middle lamella is destroyed and the fibres isolated; but it is not so well known that _not every water_ is suitable for this “retting” or steeping process; and for a long time this was as much a mystery as why some waters are so much better than others for brewing. Quite recently Fribes has succeeded in isolating the bacillus upon which the dissolution of the middle lamella depends. This investigation brought out other interesting details as to the reaction produced by living micro-organisms, and which can be utilised in deciding questions of plant chemistry too subtile for testing with ordinary re-agents. One other important fact connected with these researches is that botanists have now discarded the view that the middle lamella of the plants referred to is composed of cellulose, and know that it consists of pectin compounds. Fribes’ anærobic bacillus is found to dissolve and destroy pectins and pectinates, but does not touch cellulose or gum. It is well known that the steeping of skins in water in preparation for tanning involves bacterial action, owing to which the hair and epidermal coverings are removed, but it also appears that in the process of swelling the limed skins, the gases evolved in the substance of the tissues, and the evolution of which causes the swelling and