CONDITIONS OF CELL REPRODUCTION. 227 



D. P. HOYER (I.) by fixing a small number of cells, in a state of 

 watery suspension, on a thin film of solidified wort-gelatin applied 

 to the under side of the cover-glass of a Bottcher cell. The pre- 

 parations, which could be examined and counted direct, were 

 maintained at the desired temperature for a certain time, the 

 cells produced in the interval being then counted and the period 

 of generation calculated by means of the formula already men- 

 tioned. The following results were obtained at 13 C. : Sacch. 

 Pastorianus /., Hansen, 6 h. 6 min. ; 8. Past. II., 8 h. 45 min. ; 

 8. Past. III., 8 h. 39 min.; 8. ellipsoideus /., 9 h. 4 min.; ~S. 

 ellips. II., 8 h. 49 min. ; S. anomalus, 5 h. 12 min. ; S. Ludwigii, 

 8 h. 10 min.; S. membrancefaeiens, 7 h. i min.; Saaz yeast, 

 7 h. 48 min.; Frohberg yeast, 7 h. 21 min.; Sacch. apiculatus t 



4 h. 45 min., &c. The period of generation at 25 C. was, for 

 8. Past. II., 5 h. 12 min. ; S. Past. III., 6 h. 8 min. ; S. ellips. /., 

 6 h. 12 min.; S. ellips. II., 6 h. 9 min.; S. membrancefaeiens, 



5 h. 13 min. ; Saaz yeast, 4 h. 23 min. ; Frohberg yeast, 4 h. 18 min. 

 In the same proportion as new cells are formed, the medium is 

 impoverished of the necessary structural materials and enriched 

 with metabolic products inimical to development. Both these 

 influences grow quicker when the nutrient medium is kept warm, 

 and then soon become so powerful that the velocity of reproduction 

 falls below the value previously obtained from cultures that have 

 been kept much cooler, while at the same time the period of 

 generation is correspondingly increased. Thus in Pedersen's 

 experiments, cited above, the period of generation on the second 

 day, though 20 hours at 4 C. and 16.7 hours at 13.5 C. was 

 increased to 65,5 hours at 23 C. Further details \\ill be 

 given on this point in that portion of the next chapter which 

 deals with the influence of alcohol on the life of yeast. In the 

 case of temperatures near the limits beyond which budding ceases, 

 the velocity of reproduction is so low as to be regarded as nil from 

 the practical standpoint, H. MULLER-THURGAU (XIX.) having 

 reported, for instance, that the wine yeasts examined by him 

 ceased to reproduce at 40 C. In climates where the temperature 

 at the time of the vintage approaches this limit the South of 

 France, for example, according to KAYSER and BARBA (I.) the 

 must has to be artificially cooled, or the yeast cells present will 

 reproduce so slowly that only a sluggish fermentation will be set 

 up, incapable of suppressing concomitant injurious organisms. 

 In northern vineyards, on the other hand, the autumn temperature 

 not infrequently approaches the lower limit for yeast reproduction ; 

 and in that event the fermentation of the must is greatly retarded 

 and slow. 



In breweries using low-fermentation yeast the wort is pitched 

 at 5-7-5 C., and during primary fermentation the temperature 

 is not allowed to exceed 9 C. for beer of the Bohemian type, 

 9.5 C, for Vienna beer, or 10.5 C. for Bavarian beer; so that 



