When caseous ferment is sown in a saccharine medium charged with mineral salts, its aspect, form, and mode of budding differ completely from what they are when the ferment exists in a natural medium, such as wort or other liquid adapted to the nutrition and life of ferments. [Illustration: Fig. 46.] Fig. 46 represents this ferment in course of development, forty-eight hours after it had been sown in a saline medium (we employed Raulin’s fluid, substituting bi-tartrate for the nitrate of ammonia). It will be seen how different its aspect is from that of the preceding figures; it is still capable, however, of resuming the forms of the latter if cultivated afresh in natural saccharine worts. “High” yeast from a “high” fermentation brewery in the Ardennes, after having been exposed to heat under the conditions given above, likewise produced caseous ferment, without a trace of “high” ferment, just as happened in the case of the Dutch yeast. All the “high” yeasts used in brewing seem to behave in the same manner. What conclusion are we to draw from these facts? Apparently that “high” yeast is modified by heat in an acid and alcoholic medium, giving rise to caseous ferment. On the other hand, it might be conceived that the “high” yeasts on which we experimented were not pure, but contained, in a state of intermixture, some caseous ferment, and that by the application of a temperature of 50° C. (122° F.) to our alcoholic medium, the high ferment was all killed and the caseous ferment alone survived. It is a remarkable fact that this latter hypothesis, improbable as it seems, inasmuch as the microscope revealed no intermixture of ferments, seems, nevertheless, to be a true one. As a matter of fact, if we subject to a temperature of 50° C. for one hour in the medium in which it acts, not the “high” yeast of commerce but “high” yeast that is _absolutely pure_, this will perish utterly, and the wort after cooling may remain for years in an oven without either undergoing fermentation or developing any growth whatever of “high” ferment or “caseous” ferment. On the other hand, if we impregnate this same alcoholic liquid with some of the caseous ferment and then heat the vessel to 50° C. for one hour, the caseous ferment will go on reproducing itself after the liquid has cooled down.[106] It seems, therefore, impossible to admit that caseous ferment results from a modification of “high” ferment, and we are led to believe that in the preceding experiments it must have been the progeny of cells of caseous ferment present in the “high” yeasts of commerce, which cells, probably in consequence of their scarcity, the microscope was unable to reveal, but which, nevertheless, did exist, and went on reproducing themselves alone after the heating. [Illustration: Fig. 47.]