This conclusion is supported by the following fact, which also tends to prove that in the case of the “high” English _pale ales_, caseous ferment plays a most important part. In the medium already described, we sowed the deposit from a bottle of good English pale ale. After having been heated the yeast went on growing, and we obtained the very beautiful specimen of caseous ferment represented in Fig. 47. The two dark globules are dead cells which had been killed. Two minute segments of lactic ferment are also visible in the sketch—the yeast which we sowed was, of course, impure—and their presence proves, we may observe, by the way, that lactic ferment also can withstand a temperature of 50° C. (122° F.) in the medium which we here employed. The yeast as sowed is represented in Fig. 48; it reminds us forcibly of certain forms of the caseous ferment. Amongst the globules, which for the most part were transparent and very young, there were some which appeared aged and of a yellowish colour and granular. These latter probably belonged to the yeast of manufacture. Their shape distinguishes them from “high” yeast, properly so called, as on the other hand it causes them to appear more like cells of a recent growth to which, there is no doubt, beer, after it is put in bottle, owes its effervescence and head. These various circumstances incline us to believe that the caseous ferment forms part of certain commercial yeasts, especially those used in the celebrated breweries of Bass and Allsopp, at Burton-on-Trent, in the manufacture of pale ale. Caseous yeast is, moreover, a “high” ferment, that is to say, it rises to the surface. [Illustration: Fig. 48.] § V.—On a New Race of Alcoholic Ferments: Aërobian Ferments. Mention has already been made of certain researches which we undertook with the object of ascertaining whether _mycoderma vini_, or efflorescence of wine, and _mycoderma cerevisiæ_, or efflorescence of beer, which grow equally well in all fermented liquids, have the power of becoming transformed into actual alcoholic ferment. The result of those researches was stated to be that these mycodermata do not become transformed into ferment, properly so called, and that whenever any such transformation has been supposed to have taken place, the ferment produced was derived from germs introduced by the air or by the utensils employed. What we did ascertain of the ferment-producing power of _mycoderma vini_, was merely that this plant, when submerged, is capable of causing sugar to ferment, in consequence of a certain continuous life possible to its cells, apart from the oxidations resulting from the presence of free oxygen, but without any generation of new cells taking place.