No. 1 of the engraving represents the ferments of _turned_ beer, as it is called. These are filaments, simple or articulated into chains of different size, and having a diameter of about the thousandth part of a millimetre (about 1/25000 inch). Under a very high power they are seen to be composed of many series of shorter filaments, immovable in their articulations, which are scarcely visible. In No. 2 are given the lactic ferments of wort and beer. These are small, fine and contracted in their middle. They are generally detached, but sometimes occur in chains of two or three. Their diameter is a little greater than that of No. 1. In No. 3 are given the ferments of putrid wort and beer. These are mobile filaments whose movements are more or less rapid, according to the temperature. Their diameter varies, but is for the most part greater than that of the filaments of Nos. 1 and 2. They generally appear at the commencement of fermentation, when it is slow, and are almost invariably the result of very defective working. In No. 4 are given the ferments of viscous wort, and those of ropy beer, which the French call _filante_. They form chaplets of nearly spherical grains. These ferments rarely occur in wort, and still less frequently in beer. No. 5 represents the ferments of pungent, sour beer, which possesses an acetic odour. These ferments occur in the shape of chaplets, and consist of the _mycoderma aceti_, which bears a close resemblance to lactic ferments (No. 2), especially in the early stages of development. Their physiological functions are widely different, in spite of this similarity. The ferments given in No. 7 characterize beer of a peculiar acidity, which reminds one more or less of unripe, acid fruit, with an odour _sui generis_. These ferments occur in the form of grains which resemble little spherical points, placed two together, or forming squares. They are generally found with the filaments of No. 1, and are more to be feared than the latter, which cause no very great deterioration in the quality of beer, when alone. When No. 7 is present, by itself or with No. 1, the beer acquires a sour taste and smell that render it detestable. We have met with this ferment existing in beer, unaccompanied by other ferments, and have been convinced of its fatal effects. No. 6 represents one of the deposits belonging to wort. This must not be confounded with the deposits of diseased ferments. The latter are always visibly organized, whilst the former is shapeless, although it would not always be easy to decide between the two characters, if several samples of both descriptions were not present. This shapeless deposit interferes with wort during its cooling. It is generally absent from beer, because it remains in the backs, or on the coolers; or it may get entangled in the yeast during fermentation and disappear with it.