228 



T. NAKAMURA ; ON THE BEHAVIOUR OF 



My own experiments were made with pure cultures obtained 

 from a single colony on a sugar gelatine plate and with cells free 

 from ascospores. From such yeast grown in a solution of lo% cane 

 sugar with 0.^% meat extract, the supernatant liquid was decanted 

 off, the sediment washed with sterilized distilled water to remove 

 the nutrients and the alcohol produced, as these substances might 

 perhaps have interfered with the result. The yeast so treated 

 was suspended in some sterilized distilled water and 5 c.c. of this 

 mixture, placed in a narrow sterilized test tube provided with 

 a cotton plug, w^ere exposed for several minutes to a constant 

 temperature in a water bath. 



It was thus found that the fermenting power was not destro)'- 

 ed even when the yeast A\ as exposed for an hour and a half to 

 46°C., or for one hour to 48°C. However, at a temperature of 

 52°C. the fermenting power was wholl}' destroyed w^ien the 

 exposure was kept up for more than 20 minutes ; nor was any 

 development on a gelation plate noticed. 



In order to reach results as exactly as possible in regard to 

 the thue necessary to destroy the fermenting power at 50°C. I 

 proceeded as follows : A number of test tubes containing jjure- 

 cultured yeast in sterilized distilled w^ater were first placed in a 

 vessel containing water of about 55°C., and the tubes were con- 

 tinuously well shaken ; one of these tubes containing only water 

 was provided with a delicate thermometer. When a temperature 

 of 50'^C. was reached, all the tubes were placed in another vessel 

 containing water of a constant temperature of 50°C. Every five 

 minutes one of the tubes was removed, and after cooling 5 c.c. of 

 sterilized Pasteur s solution of double the ordinary strength were 

 added and the mixtures kept in an incubator at 16° — 25°C. I 

 then observed that a duration of 25 minutes had not destroyed 

 the fermenting power, but that after 30° minutes the destruction 

 was completely effected. 



In order to determine the point more precisely, I repeated 

 the same operation at intervals of only one minute between the 

 25 — 30 minutes. 



The result was that even 29 minutes exposure to 50°C 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 nourish- 

 ing solutions. 



