ORGANIC SOURCES OF NITROGEN. 217 



by the latter ; if soluble, it remains in the liquid, but if trans- 

 formed into the insoluble condition it will be found in the sedi- 

 mental yeast. The quantity of the soluble matters excreted from 

 the cells increases with the temperature, other conditions being 

 equal. The experiments of E. HANTKE (I.) on this point showed, 

 for example, that beer produced from a wort containing 5.59 per 

 cent, of nitrogenous substances, by means of one and the same 

 type of yeast, contained 4.42 per cent, of these substances when 

 fermented in the cool cellar of the brewery, and 5.10 per cent, 

 when the fermentation was completed in the laboratory (at 66 F.). 

 The characteristic disagreeable flavour produced in beer by fer- 

 mentation at an unduly high temperature is due to this increased 

 formation of metabolic flavouring products, which will be the 

 more noticeable in proportion as the other (flavouring) extract 

 constituents is smaller. For this reason beers of this class 

 (especially Pilsen) must be fermented at a lower temperature 

 than those of the Bavarian type. 



Finally, it should be mentioned that the fact of the migration 

 of nitrogenous substances from the yeast to the nutrient medium 

 renders illusory the results of all investigations in which it is 

 sought to ascertain the quantity of nitrogenous matter assimilated 

 by yeast from the difference in the nitrogen content of the medium 

 at the beginning and end of the experiment. Consequently, this 

 question also needs rein vestigat ion by the application of more 

 delicate methods of experiment. 



