22 6 CULTIVATION AND REPRODUCTION OF YEAST. 



reproduction" or "reproductive energy") indicates the number of 

 cells produced from the unit of sowing in unit time. With regard 

 to the determination of this value, the remarks just made also 

 apply. 



By the " period of generation " is generally understood the 

 interval of time necessary for the production of a fully developed 

 daughter cell from the parent cell by budding. If F. BASENEAU'S 

 formula (I.) (vol. i. p. 59) is used for this determination, instead 

 of the method of direct observation of the individual cell, it must 

 be remembered that this formula does not strictly apply, except 

 under the condition that the duration of generation has been the 

 same for all cells in the culture throughout the whole experiment, 

 and that each newly formed daughter cell has immediately begun 

 to act as a parent cell. Since this latter condition in particular is 

 not usually fulfilled in its entirety, the value furnished by the 

 calculation is higher than the truth. 



The influence of temperature on cell reproduction by budding 

 deserves very close consideration, because the use in practice of 

 nutrient media which are mostly of almost constant and unchange- 

 able constitution, renders it possible to control the progress of 

 reproduction by graduating the influence in question. The limits 

 of temperature within which cells will bud in beer wort have 

 been determined by E. C. HANSEN (XXXII.) for eleven different 

 Saccharomycetes. The upper limits were : for Sacch. Past. /., 34 C. ; 

 for Sacch. niembrancefaciens, S. Ludwigii, and Wortmann's wine 

 yeast, Johannisberg II., 37 C. ; for 8. cerevisice /., S. Past. II. 

 and S. ellips. //., 40 C. ; for S, ellips, /., 40-41 C. ; and for S. 

 Marxianus, 46-47 C. ; whilst the lower limits were as follow : 

 S. cerevisice I. and S. membrancefaciens, 3 to i C., S. anomttlus, 

 IC. to 0.5 C., and for the other eight species o.5C. Acomparison 

 of these figures with those in the table opposite p. 136, vol. ii., 

 will confirm the remark on pp. 129, 130, that the limits of 

 temperature are somewhat wider in the case of budding than for 

 sporulation, provided the former occurs in wort. If, on the other 

 hand, the cells be allowed to bud in water, the higher limit of 

 temperature is slightly reduced, whilst the minimum is raised. 

 Saccharomycopsis guttulatus will only bud at 37 C. 



The influence of temperature on the period of generation was 

 first closely investigated by RASMUS PEDERSEN (II.), after a few 

 observations on the subject had been communicated by Pasteur 

 and others. Working with a low-fermentation beer yeast in un- 

 hopped wort (16.2 Balling), Pedersen found that the duration of 

 generation in the first 24 hours of development was 20 hours at 

 4 C., loj hours at 13.5 C., 6J hours at 23 C., 5.8 hours at 

 28 C., and 9 hours at 34 C., no budding occurring at 38 C. 

 Consequently, the optimum temperature giving the shortest period 

 of generation in these experiments was between 28 and 34 C. 

 At a later date a more comprehensive test was performed by 



