242 PHYSIOLOGY OF BACTERIA 



nomical to feed the yeast on ammonia alone, it is quite 

 advantageous to feed ammonia besides organic nitrog- 

 enous matter. A great drop in the yeast crop, if the 

 last of the organic nitrogen is taken away, is very 

 conspicuous in Table 67. 



These results are enlarged by a number of other 

 experiments. Numbers 16 and 17 are directly com- 

 parable with the above, having a total available nitrogen 

 of 3.5 gm. Numbers 7, 8, and 9 are comparable with 

 each other, showing the differences in the availability 

 of asparagin, aspartic acid and ammonia. 



In nitrogen-free sugar solution, (Exps. 10, 11, and 12) 

 the yeast loses nitrogen. Exps. 22 and 23 show that in 

 ''spent" wort, practically all available nitrogen had been 

 assimilated by the first crop, and that after addition of 

 more sugar, only a small amount of the total nitrogen 

 could be used by the second crop. 



When ammonia is used as the only source of nitrogen (Exp. 18), 

 the crop is small, but the yeast is high in protein content. This is 

 typical for all yeasts grown with ammonia. 



Table 66. — Nitrogen Content in Yeast Solids 

 Yeast with ammonia 



Whether this higher nitrogen content is stored protein, we have no 

 means of telling. It does not mean an increase in zymase, for the 



