Side by side with the facts explained in the last paragraph, the study of varieties of the genus _mucor_, grown in natural or artificial saccharine liquids, is of great importance to the establishment of the physiological theory of fermentation, which we shall explain later on. There is a very remarkable work on the subject of this mucedinous fungus by a German botanist, M. Bail, who, in 1857, declared that _mucor mucedo_ caused alcoholic fermentation, and could change into ordinary yeast. The first assertion, relating to the alcoholic fermentation that this fungoid growth which is everywhere so abundant may cause, is quite correct; the second which relates to its faculty of changing into yeast is erroneous.[75] On June 13th, 1872, we sowed by the help of a platinum wire in some wort, contained in two-necked flasks, A, B, and C, several of the minute sporange-bearing filaments of _mucor_ along with the heads containing the spores. On June 14th, there was no mycelium visible to the naked eye in the liquids. On June 15th mycelium was very abundant, and was borne up by bubbles of gas. In addition to this there were a few scattered patches of bubbles on the surface of the liquid, showing that fermentation had commenced. On June 16th fermentation continued to show itself by the frothy state of the crusts of mycelium buoyed up by the bubbles of gas. On June 17th we attached B and C separately, as indicated in Fig. 19 (p. 101) to test-flasks, into which we transferred nearly all their contents. Some clusters of entangled filaments of mycelium remained on the surface of the liquids in the test-flasks. On June 18th a very slow fermentation commenced in the test-flasks; it continued for some days without becoming more active. A little bubble would slowly rise from the bottom of the vessel, succeeded after a short interval by another, and so on. The temperature of the oven was 24° C. (75° F.). On June 22nd we raised it to 28° C. (82° F.). The fermentation became more rapid, a constant succession of bubbles rose quickly from the bottom of the test-flasks; still there was none of the vivacity of an alcoholic fermentation produced by yeast. On June 25th the fermentation was in much the same condition, if anything rather less active. On June 28th temperature 25° C. (77° F); fermentation had stopped. On June 29th we raised the temperature to 27° C. (81° F.) again, and some slight revival of fermentation manifested itself. The increase in temperature, therefore, as might have been expected, exercises a considerable influence on this kind of fermentation. The vessels were then left to themselves, and during the course of three months they did not show the least sign of fermentation; moreover, we did not observe, either on the interior walls of the empty flasks, or on the surface or throughout the body of the liquid in the test-glasses, any fungoid production or organism whatever different from _mucor_ itself.