164 MICRO-ORGANISMS AND FERMENTATION. 



Pastorianus species will die in the course of eleven days, whilst 

 Sacch. cerevisice I. and the two ellipsoid species will still be 

 living. From this result it is evident that the statement 

 formerly accepted that top-fermentation yeasts can develop at 

 higher temperatures than bottom yeasts is incorrect. 



KAYSER'S more recent experiments confirm these results, and 

 also show that yeasts can resist a considerably higher tempera- 

 ture in a dry state than in the presence of moisture. For 

 instance, a pale ale yeast was killed when exposed for five 

 minutes in a moist condition to a temperature of 60 to 65 C., 

 but when dry, it withstood a temperature of 95 to 105 C. ; 

 in the case of a wine yeast (St. Emilion) the temperatures 

 were 55 to 60 C. and 105 to 110 C. The resisting power 

 of the spores was 10 to 20 higher. 



Vegetative cells which had developed from the heated spores 

 exhibited a somewhat greater power of resistance than normal 

 vegetative cells. This increased resistive power was, however, 

 not transmitted further, and, on cultivation in beer-wort, 

 disappeared even in the second generation. 



(e) Cultivation on a Solid Nutritive Medium. HANSEN 

 discovered distinct characteristics for several species of the 

 Saccharomycetes by suitable cultivation on a solid nutritive 

 medium. For this purpose he employed small flasks contain- 

 ing wort, to which about 5*5 per cent, of gelatine had been 

 added, the flasks being closed by means of cotton-wool plugs. 

 When these flasks are inoculated with the six known species 

 (Sacch. cerevisice /., Sacch. Pastorianus I., //., III., Sacch. 

 ellipsoideus /., //.), and set aside at a temperature of 25 C., 

 the growths which develop show such macroscopic differences, 

 in the course of eleven to fourteen days, that four groups may 

 be more or less sharply distinguished. Sacch. ellipsoideus I. 

 stands alone, for its growth exhibits a characteristic net-like 

 structure on the surface, which enables this species to be 

 distinguished by the unaided eye from the other five species. 

 When gelatine with yeast-water is employed for such 

 cultures and the experiment conducted at 15 C., Sacch. 

 Pastorianus II. yields growths, after the lapse of sixteen days, 

 the edges of which are comparatively smooth, whilst the 

 growths obtained from Sacch. Pastorianus III. are distinctly 



