Author Description

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1898 edition. Excerpt:...29 minutes exposure to 5OC did not destroy the fermenting power, while in 30 minutes it was again completely done. Further no trace of development was noticed, when this yeast was transfered into well aerated nourishing solutions. An observation was, however, made during all these experiments 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 retardation 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 5OC. 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 5OC., still preserved all their vital powers and were observed to develop well, when inoculated on nourishing gelatine, potato, or in i% sugar and pepton solution. I, therefore, infer that for 25 minutes a temperature of 50 forms the limit beyond which not only the fermenting power but also all other life functions are destroyed. It was my further object to test the influence of various compounds upon the resisting power of the yeast-cells against heat. The experiments were carried on in the same way as described above, but the yeast 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 Effect after the addition of...