ORGANIC SOURCES OF NITROGEN. 215 



originally present in a given wort was eliminated by means of a 

 large sowing of yeast, coupled with rousing and agitation, whereas 

 with a medium sowing without aeration only 17.2 per cent, was 

 removed, and merely 15.8 per cent, with a small sowing and slight 

 aeration. 



The influence of the nature of the source of nitrogen is revealed 

 by the observation made by A. L. STERN (Y.) that in parallel 

 cultures with equal initial nitrogen content, either in the form of 

 asparagin, peptone or yeast extract, the relative quantities of this 

 element eliminated by the yeast were i : 1.8 : 2.2. That the amount 

 of sugar present in the nutrient medium also influences the ab- 

 sorption of nitrogen has been shown by P. THOMAS (I.) and also by 

 STERN (III.) The former observer found that a larger quantity 

 of the urea offered as the source of nitrogen was assimilated in 

 presence of 20 per cent, of dextrose than when only 10 per cent, 

 of that sugar was available. In Stern's experiments the largest 

 quantity of asparagin was assimilated from a mineral-salt solution 

 containing 0.3 per cent, of that substance when the added dex- 

 trose amounted to 15 per cent, (the limits ranging from o to 30 

 per cent.) ; but when only 0.15 per cent, of asparagin was present 

 the optimum quantity of sugar fell to 12.5 per cent. 



Apart from the exceptions to be mentioned hereafter, all the 

 worts, musts, and mashes fermented on a practical scale contain a 

 surplus of nitrogenous nutriment ; so that this is still far from 

 being exhausted by the time cell-reproduction has come to a stand- 

 still in consequence of the gradual change for the worse in the 

 other conditions of nutrition, especially by the increased alcohol 

 content (see chapter Hi.). Hence a larger or smaller quantity of 

 useful nitrogenous nutriment remains in the fermented product. 

 As we have been informed by J. VON LIEBIG (II.), Graham, A. W. 

 Hoffmann, and Redwood in 1853 found that pale English worts 

 containing 0.217 per cent, of nitrogen furnished beers containing 

 0.134 per cent. Similar investigations also with infusion worts 

 in an English brewery were made by H. GRIMMER (I.), with the 

 result that, of the nitrogen (0.132-0.138 per cent.) in the original 

 wort, about one-fourth (2426 per cent.) was found to have been 

 taken up by the yeast, the greater portion (one- half to two-thirds) 

 being absorbed during the first twenty to twenty-four hours after 

 pitching. This was confirmed by C. F. HYDE (I.). Substantially 

 the same observation was made by DELBRUCK (I.) in the case of 

 pressed yeast in 1879, so that the nitrogen consumption curve 

 rises very sharply. One pressed yeast and three different samples 

 of low-fermentation beer yeast (containing 8.24 and 8.94 to 9.54 

 per cent, of nitrogen in the dry residue), which were allowed by 

 HAYDUCK (V., VI.) to develop under identical conditions in malt- 

 extract solution containing initially 0.0876 per cent, of nitrogen, 

 absorbed 43 and 30-39 per cent, of this foodstuff for the struc- 

 tural purposes of the cell. That the residual nitrogenous substances 



