246 PHYSIOLOGY OF BACTERIA 



foods belong not only carbohydrates and the like, but 

 also oxygen. Attention has already been called to the 

 experiments of A. J. Brown (p. 233) proving the oxygen 

 concentration to be quite essential for a large crop of 



yeast. 



Of the large amount of literature on the yields of yeast under 

 varying conditions, very little can be used here, because it is cus- 

 tomary in the yeast industries to record the crop in relation to the 

 seeding, and not in absolute values; it is stated, e.,g. that the yeast 

 multiplied five to eight times. This method of measurement is 

 meaningless except for the direct comparison of two experiments 



^ 



4% 3u.qt 



S% SttqcLr- 



ar 



Z% Suf€er 



/U Suyocr 



ti\ 



i/rie 



Fig. 24. — Theoretical growth curve of yeast with abundant building material 

 and increasing amounts of sugar. 



with the same seeding in the same medium. Even the scientists 

 resort to this method when working on yeast problems (A. J. Brown, 

 Lafar, Henneberg). 



The theory of the influence of food concentration is 

 fairly simple. Building material that does not contain 

 a source of energy will produce no growth; nor will a 

 source of energy that contains no building material 

 induce growth; both are needed. 



