ORGANIC SOURCES OF NITROGEN. 213 



whereas in the case of peptone they unite into flocculent masses, 

 which settle down less firmly than the others, was also con- 

 firmed by H. LANGE (I.) with beer wort, his explanation being 

 that the cohesion is due to precipitated peptone. A high selec- 

 tive power is exerted by Schizosacch. octosporus, which, according 

 to BEYERINCK (XVIII.) is suited only by the nitrogen compounds 

 naturally present in raisins or malt, and not by ammonium salts, 

 asparagin or peptone. 



Among cereal grains, rye is characterised by a high percent- 

 age of proteins specially suitable for the formation of yeast 

 protoplasm. This is one of the reasons why yeast manufacturers, 

 particularly those working with the old (Vienna) method, prepare 

 their mashes with an addition (usually one-third) of this grain. 

 Its percentage content of nitrogenous substances fluctuates, how- 

 ever, betwen wide limits, 7.5 per cent, on the one hand and 15.3 

 per cent, on the other, being by no means exceptional figures as 

 was shown by DELBRUCK (IV.) in a highly interesting experiment. 

 Manufacturers endeavour to counteract the resulting great varia- 

 tion in the amount of the yeast crop by employing mixtures of 

 rye of different origin ; but they would, no doubt, prefer to be 

 able to determine the amount of these proteins in buying the raw 

 material, and to value the latter accordingly. On this point, how- 

 ever, there are no data at present available. Among the proteins 

 and allied substances mention should also be made of diastase, 

 which is not merely capable of serving as a source of nitrogen 

 when present as the sole nitrogenous constituent of the nutrient 

 medium, but is also taken up and utilised by the yeast, and thereby 

 caused to disappear, even when peptone and aspaiagin are also 

 present in sufficient quantity. This observation, recorded by 

 HEINZELMANN (IV.), is of interest in connection with the fer- 

 mentation of raw grain (maize, &c.) mashes, in which the unsac- 

 charified dextrin is intended to be hydrolysed by diastase during 

 the prolonged primary fermentation. In one experiment per- 

 formed by HEINZELMANN (V.), out of the 37 parts of diastase left 

 from each 100 originally present at the end of the mashing process, 

 33.4 disappeared during fermentation, so that only 3.6 remained 

 in the fermented mash. 



When amides are present in nutrient media together with 

 proteins and their nearest degradation products, the selective 

 power of the cells (see p. 46, vol. i.) becomes manifest. In this 

 connection a number of very instructive data are already available. 

 The degradation products of protein are always present in brewery 

 and distillery mashes, owing to the activity of the proteolytic 

 enzymes in the malt used. In an experiment performed by C. J. 

 LINTNER (V.), out of the total nitrogen (0.092 per cent.) in the 

 saccharified malt extract used as the nutrient medium, and com- 

 posed of 0-062 per cent;, of amides and 0.030 per cent, of proteins, 

 &c., 0.036 per cent, (viz., 0.030 per cent, of amide nitrogen and only 



