228 MICRO-ORGANISMS AND FERMENTATION. 



proved by exhaustive experiments that it is not sufficient to 

 supply nitrogen in inorganic compounds. Kossowicz reached 

 the same conclusion, and showed that by sowing a single cell 

 in a saccharine fluid containing mineral matter no development 

 took place, whilst with a greater infection of cells development 

 may proceed. 



It has been definitely proved in the case of the Mycoderma 

 species that their demand for nitrogen can be fully satisfied 

 by ammonia in the form of inorganic compounds. 



Organic nitrogenous compounds occur in considerable 

 quantities in most of the liquids fermented in practice. Thus 

 the cereals which are utilised in breweries and distilleries 

 contain a series of proteins which possess a nutrient value for 

 the yeast cell. Rye is specially rich in these substances, and 

 for this reason an admixture of this cereal is always used in 

 the manufacture of yeast. Peptones and amides are formed 

 during the mashing process, both of which appear to be ab- 

 sorbed by yeast with special facility. Asparagin, which is 

 present in considerable quantities in sprouted corn, malt, and 

 potatoes, plays an important part as a source of nitrogen ; 

 the yeast converting it into protein. Cider musts are notably 

 poor in nitrogenous food for yeasts. Miiller-Thurgau, there- 

 fore, recommends the addition of ammonium chloride (about 

 20 grammes per hectolitre) or of ammonium tartrate. 



A large number of analyses have been made to determine 

 the albuminoid contents of yeast. Wijsmann found that the 

 proportion varies greatly, even at different stages of fermenta- 

 tion. At first the quantity of nitrogen rises rapidly, but 

 afterwards it gradually diminishes. Thus the nitrogen may 

 rise from about 7 to 10 per cent., calculated on the dry sub- 

 stance, during the first hour. Amongst the albuminoids, 

 special reference must be made to the nucleins, substances 

 which owe their name to the fact that they are the principal 

 constituents of the nucleus of the yeast cell. They were shown 

 to be present in considerable quantities in Kossel's extensive 

 researches on pressed yeast, and others have since demon- 

 strated their presence in yeast. They are very complex 

 substances, and appear to play an essential part in the develop- 

 ment of the yeast cell (division of the nucleus). Their occur- 



