256 MICRO-ORGANISMS AND FERMENTATION. 



those previously mentioned. Such an enzyme (amylase) has 

 been detected in a few moulds. 



Amongst the enzymes found by Buchner and Hahn in 

 yeast-juice, the proteolytic enzyme or endotryptase plays an 

 important part in the life of the cells, especially during the 

 so-called auto-fermentation. Its presence was mentioned in 

 the early literature of the subject. Its optimum is at 40- 

 45 C., and it is completely destroyed by one hour's heating 

 at 60 C. In a dry condition it is more resistant. It can 

 withstand the action of weak antiseptics, and weak acids. 

 Neutral salts react favourably. Saccharose, even in a 5 per 

 cent, concentration, restricts its activity, and in a 35 per cent, 

 concentration it is completely arrested. Will examined a series 

 of yeasts, and proved that the rate at which they liquefy 

 gelatine is variable, and that those' that act rapidly are also- 

 those that require a free supply of oxygen. 



Reducing enzymes are also found in yeast cells, and 

 amongst these must be classed the enzyme which converts 

 sulphur into sulphuretted hydrogen.* According to Nastukoff, 

 Osterwalder, Schander, Will, and others, it occurs in very 

 different degrees of activity in the various yeast species. 



A clotting enzyme in yeast has been detected by Rapp. 



The Action of the Saccharomycetes and similar Fungi on 

 Carbohydrates and other Constituents of Nutritive Liquids. 



Diseases in Beer. 



The first decisive proof that species of Saccharomyces may 

 produce very different reactions on the nutritive liquid was 

 given by means of pure cultures of yeasts prepared by E. C. 

 Hansen in 1883, and afterwards by the author. 



* Both in beer and wine a formation of sulphuretted hydrogen occurs (in the 

 latter case called " Bockser "), more particularly at the end of the fermentation.. 

 As both the grapes and the wine and beer casks are treated with sulphur, it can 

 find its way into the liquid, but even in the absence of free sulphur or sulphur 

 compounds, the albuminoids of the nutritive liquid and the contents of the cell 

 protoplasm ir>ay provide material for the formation of sulphuretted hydrogen. 

 Certain experiments appear to indicate that a diseased condition of culture yeasts- 

 may be connected with this fact. 



