STUDIKS ON FERMENTATION. 203 



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 con- 

 ditions 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 ? Ap- 

 parently 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 tempera- 

 ture of 50° C. for one hour in the medium in which it acts, 

 not the " high " yeast of commerce but "high" yeast that is 

 ahsolutely pure, this will perish utterl}'-, and the wort after 

 cooling may remain for years in an oven without either under- 

 going 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.* 



* The caseous ferment, however, must not be exposed to heat, under 

 the afore-mentioned conditions, when it is too yoang. At the commence- 

 ment of its development, for instance, within a few days of having been 

 sown. In such case, it would be in danger of perishing, probablj' in con- 



