THE BLASTOMYCETES 163 



He claims for the solution greater activity and stability 

 than that prepared by the usual method. 



Zymase shows extreme instability, apparently due to a 

 powerful proteolytic enzyme (endotryptase or endotrypsin), 

 always present in yeast- juice, which, when digesting the 

 coagulable protein, doubtless digests the zymase at the 

 same time. The activity of zymase seems to be absolutely 

 dependent on a co-enzyme, that withstands the tempera- 

 ture of 100 C. (thermostable) and is dialysable, but of 

 which the constitution and function are unknown. 

 Harden has shown the presence of phosphates is also 

 necessary. 



The juice extracted from yeast also contains rennin, 

 a glycogen-hydrolysing enzyme, and a reducing enzyme 

 which can liberate sulphuretted hydrogen from sodium 

 thiosulphate and decolorise methylene blue. The yeast 

 cell possesses special ferments capable of destroying 

 zymase and its co-enzyme, also an anti-enzyme which 

 prevents such destruction. See also Harden' s ' Alcoholic 

 Fermentation ' (Messrs. Longmans' * Monographs of 

 Biochemistry '). 



8. cerevisice ferments saccharose, maltose, and dextrose. 

 When the alcohol produced reaches 12 per cent., growth 

 stops, and with 14 per cent, fermentation ceases altogether. 



Saccharomyces Ellipsoideus. The yeasts classed under 

 this name are bottom fermentation forms, and are usually 

 rounded or ellipsoidal in shape, but sometimes assume 

 a sausage form. The cells average about 6 // in length, 

 are single or united in little branching chains. Two to 

 four spores are found in a mother cell, each 3 fj, to 3-5 /u, 

 in diameter (twenty- one to twenty- seven hours at 25 C.). 



S. ellipsoideus I. is found on ripe grapes, and plays an 

 important part in the fermentation of grape- juice. 



S. ellipsoideus II. is a dangerous ' disease ' yeast, 

 producing yeast turbidity, in bottom fermentation 

 breweries. 



Saccharomyces Pastorianus. This yeast of which 

 three varieties, known as L, II., and III., have been 

 isolated by Hansen is very polymorphic in shape. The 

 cells are oval or sausage-shaped, and also occur in elon- 

 gated, ellipsoidal, or pear-shaped forms. Two to four 

 spores are usually found in a mother cell (twenty-five to 

 twenty-eight hours at 25 C.). They take a part in many 



