YEAST AT A HIGH TEMPERATURE. 



229 



An observation was, however, made during all these experi- 

 ments which may explain the contradictory statements of those 

 observers who claimed that the fermenting power is destroyed 

 by a temperature of 40°. I have found that yeast exposed to heat 

 for some time never showed within such short time fermentation 

 in Pasteur s solution as the control sample ; sometimes the retar- 

 dation amounted to 12 hours, sometimes to several days. 



In some of the cases mentioned, viz., when yeast was heated 

 for 27 or 29 minutes to 50^C. a weak fermentation was afterwards 

 observed with these samples but after a few days it gradually 

 stopped again, long before all the sugar of the solution was 

 fermented. But those samples of yeast that had only been 

 exposed for 25 minutes to 50'^C., still preserved all their vital powers 

 and were observed to develop well, when inoculated on nourishing 

 gelatine, potato, or in \% sugar and pepton solution. I, therefore, 

 infer that for 25 minutes a temperature of 50° forms the limit 

 beyond which not onl}' the fermenting power but also all other 

 life functions are destroyed. 



It was my further object to test the influence of various com- 

 pounds upon the resisting power of the yeast-cells against heat. 

 The experiments were carried on in the same way as described 

 above, but the } east was here suspended in different solutions 

 instead of in distilled water, while the liquid was heated. The 

 temperature was 50° and the duration 30 minutes. The results 

 were as follows : 



Solution in which the yeast 

 was heated. 



Distilled water. 

 Pasteur s solution'" 

 Cane sugar \o% 

 Meat-extract 0.5^ 

 Sodium chloride 1.2.3.5.10% 

 Sodium nitrate ,, ,, ,, 

 Sodium sulphate ,, ,, ,, 

 Di-sodium phosphate ,, ,, 



Effect after the addition of aerilized 

 Pasteur's solution. 



No fermentation. 

 Fermentation. 

 No fermentation. 

 Normal fermentation. 

 Only fermentation at 3%. 

 Only fermentation at 2%. 

 No fermentation. 

 No fermentation. 



(I) Pasteur's solution in all cases here descril ed consisted of 10% cane sugar and 

 0.5% meat-extract. 



