14-12 THE YEAST CELL 



were also made with galactose and maltose and showed the same 

 general distribution of points. 



It is evident from the figures that the same independence of 

 yield and gas production exists for single sugars as was found in 

 the three -sugar broth medium. One striking difference appears, 

 however, in the wide spread along the yield axis when single sugars 

 are used, as compared with that observed when the "3 -sugar broth" 

 was used. This is due to the fact that there are relatively few yeast 

 strains which cannot metabolize any of the three sugars used in the 

 "3 -sugar broth," whereas a fair number can be found which find it 

 difficult to grow well on glucose, sucrose, or levulose alone. For 

 all sugars examined both vigorous and poor gas producers were 

 found among the comparatively high yielding cultures. Here again 

 it is difficult to escape the conclusion that a strikingly different 

 physiology exists amongst closely related types. 



The yield and gas production of the same strains were com- 

 pared on different sugars. Figs. 14-10 to 14-12 inclusive give such 

 comparisons for gas production. In these diagrams both coordin- 

 ate axes represent units of gas produced, the abscissae corres- 

 ponding to behavior on one sugar, the ordinate being used for the 

 other. The relative distances of any given point from the two axes 

 denote then the comparative behavior of the corresponding strain 

 on the two carbohydrates being compared. Points lying on or close 

 to the 45 degree line drawn in each diagram correspond to strains 

 which can handle the two sugars equally well. 



As is illustrated by the even distribution about the 45 degree 

 line, fig. 14-10 shows an expected general equivalence between 

 sucrose and glucose. There are, however, a small number of 

 strains unable to ferment sucrose successfully although they have 

 no difficulty with glucose. This is probably due to a comparatively 

 low content of the sue rose -splitting enzyme in the cells of these 

 strains. Several strains demonstrate the interesting biochemical 

 character of fermenting sucrose significantly better than glucose. 

 One in particular producing 8.3 units on sucrose and only 4.1 on 

 glucose. 



The plot of sucrose against levulose given in fig. 14-11 yields 

 the same general picture as was obtained in the comparison of the 

 sucrose against glucose. Here also strains are found that can fer- 

 ment sucrose significantly better; one strain produces 8.2 units on 

 sucrose and 2.2 units on levulose. 



A comparison of the two hexoses, glucose and levulose, given 

 in fig. 14-12 reveals a small but definite shift toward the glucose 

 side. Certain strains demonstrate this preference for glucose in 

 an exaggerated manner. One strain produced 7.6 units of gas on 

 glucose and only 2.1 on levulose. 



Yield spot diagrams were also made for the same strains grow- 

 ing on the same sugars. Except for the minor movement of certain 



