GROWTH 



243 



amounts of CO2 produced average 800 c.c. for yeast grown with 

 ammonia, and 813 c.c. for yeast without ammonia. The average 

 time for softening varies greatly; it is fifty-two hours for yeast grown 

 with ammonia, and ninety-two hours for yeast without ammonia. 

 The two samples with urea are the worst ones to soften. 



These results are verified by another experiment of Claassen's 

 (1928) where increasing amounts of the assimilable nitrogen of malt 

 sprouts were substituted by ammonia. 



Table 67. — Yeast Crop and Properties with Increasing 

 Amounts op Ammonia 



Poor keeping quality and slow fermentation are characteristic 

 for yeast with a mixed nitrogen diet of from 20 to 60% ammonia. 

 The nitrogen content of the solids increases with the percentage of 

 ammonia in the food, and the total crop decreases. Whether this 

 rapid softening is due to a general weakness of constitution, or to 

 an over-supply of endo-tryptase cannot be ascertained from these 

 data. But there can be no doubt that ammonia, though it gives a 

 good crop with normal fermenting capacity, does give a yeast differing 

 physiologically from that grown on organic compounds only. 



With yeast, the final crop, as well as its nitrogen 

 content, its fermenting and keeping qualities, are 

 decidedly influenced by the nitrogenous food. This 



