ALCOHOLIC FERMENTS. 143 



at a temperature of 17 to 18 C., and in the course of eight 

 days at the same temperature had become partially dried, 

 withstood a temperature of 62 C. for five minutes, but were 

 killed at 66 C. 



In the case of Sacch. cerevisice I. the vegetative cells are, 

 under similar conditions, killed by five minutes' heating at 

 54 C., whilst at 62 C. the spores are killed. 



An interesting grouping of Hansen's six species with 

 reference to a fixed temperature is also found when they are 

 cultivated in wort under conditions favourable to film- 

 formation (see page 139). When, for instance, a temperature 

 of 36 to 38 C. is employed for the development, the three 

 Pastorianus species will be dead at the end of eleven days, 

 whilst Sacch. cerevisice I. and the two ellipsoid species will 

 still be living. From this result it is also evident that the 

 rule formerly given that top-fermentation yeasts can develop 

 at higher temperatures than bottom yeasts is incorrect. 



Later experiments made by Kayser in some of the 

 directions mentioned above confirm these results, and they 

 also show that the yeasts can resist a considerably higher 

 temperature when 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., whilst 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- 



