account of the transformation that we were seeking, which transformation we thought might possibly be that of the cells of _mycoderma vini_ into cells of ferment, generally gave us during the first days of fermentation the large, elongated, branchy ferment represented in Plate X., which was succeeded by the small ferment represented in Plate XI.[99] [Illustration: Plate 12. Ferment-cells from a Spontaneous Fermentation just starting.] Here let me describe one of these experiments. In the beginning of March, 1872, we grew some _mycoderma vini_, obtained from wine, on some wort contained in a shallow basin. On March 6th we submerged the efflorescence and put it all together, liquid and film, into a long-necked flask. On March 9th we detected incipient fermentation, and on March 12th we took a sketch of the yeast of the deposit, as given in Plate XII. This is the large and long branching, more or less pear-shaped form, which occurs at the beginning of fermentation in the sweet and acid musts of our domestic fruits. On March 16th we made another sketch of the deposit, in which the proportion of cells, in the form of elongated segments and filaments, reminded us, in some measure, of the filamentous mycelium of typical fungoid growths much diminished. In this case, however, the majority of cells were oval, round, and in short segments. On this day, March 16th, we added some fresh wort to that which had fermented, with the object of prolonging the duration of fermentation and increasing the proportion of yeast. On March 19th we made a fresh sketch, which it is not necessary either to reproduce; suffice it to say, that the yeast was now considerably more regular and uniform in appearance. [Illustration: Fig. 38.] Spontaneous ferment, therefore, very often occurs in this large ferment-form, which, by repeated developments in the act of fermentation, becomes reduced by degrees after successive generations to the ferment which, following Dr. Rees, we have named _saccharomyces pastorianus_, a polymorphous ferment which must be studied closely that it may not be confounded with others, inasmuch as it is so universally diffused that we very seldom fail to find it in any ferment which has been exposed in contact with ordinary air, at least, we may repeat, in a laboratory devoted to researches on fermentation. We have found the same thing occur in a brewery, being there mixed with the ferments used in brewing. There are, no doubt, several varieties of this _saccharomyces_. We sometimes find amongst the spontaneous ferments which repeated growths have brought to a more or less uniform state, the forms represented in Plate XI., but the cells and segments much smaller. Amongst others, Dr. Rees has distinguished a _saccharomyces exiguus_. Fig. 38 represents another spontaneous ferment, which appeared in a boiled saccharine wort, which entered into fermentation after being exposed to the air of the laboratory.