Among the shapeless granulations of No. 6 may be discerned little spheres of different sizes and perfect regularity. These are balls of resinous and colouring matter that are frequently found in old beer, at the bottom of bottles or casks; sometimes they occur in wort preserved after Appert’s method. They resemble organized products, but are nothing of the kind. We have remarked before, in “Studies on Wine,” that the colouring matter of wine would settle, in course of time, in that form. It is evident that the different ferments delineated in Plate I. are worthy of thorough study, in consequence of the fermentations to which they may give rise. Care must be taken to isolate the action of each of them in fermentations which we may call pure—a condition of some difficulty, but one that may be carried out by an adoption of the methods explained in this work. All these diseased ferments have a common origin. Their germs, infinitesimal and hardly perceptible as they are, even with the aid of the microscope, form a part of the dust conveyed through the air. This dust the air is continually taking from or depositing upon all objects in nature, so that the dust that clings to the ingredients from which our beer is manufactured, may teem with the germs of diseased ferments. During the process of fermentation, the occult power of diseased ferments, although it may escape the observation of the brewer, is manifested in a high degree. During the last thirty years, or so, the art of brewing has undergone a radical change, at least in Europe. This change has been effected by a partial abandonment of the process of fermentation formerly used. Thirty years ago only one kind of beer was known; there are nowadays two distinct kinds—beer fermented at a high temperature, and beer fermented at a low temperature. Each of these is subdivided into many varieties, to which different names are given, according to their strength or colour. This is the case in England, where we find porter, ale, pale ale, stout, bitter beer, and other varieties of beer, although, as a matter of fact, the English have but one kind of beer, all the English beers being fermented at a high temperature. Let us briefly examine the differences existing between the two kinds of beer.