138 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



The preparation of yeast juice by Buchner's method requires 

 special apparatus for obtaining high pressures which is not to 

 be found in every laboratory. It is possible, however, to 

 demonstrate the power of alcoholic fermentation, which is 

 possessed by yeast apart from its ordinary vital activity, by 

 making use of a preparation described by Albert in 1900, and 

 known as permanent yeast ('Dauerhefe') or more recently 

 zymin. This is prepared in the following way : Yeast is 

 rubbed into a powder and brought into a mixture of alcohol 

 and ether, filtered over the filter pump, and again submitted to 

 the same process of digestion with alcohol and ether and filter- 

 ing. It is then washed with alcohol and ether and finally with 

 dry ether ; on allowing the ether-wet substance to dry at air 

 temperature zymin is obtained as a fine impalpable powder. 

 On examination under a high-power microscope it will be 

 found that the finer structure of the yeast cell has disappeared. 



If, now, a small quantity of this powder is ground up with 

 a few c.c. of a warm solution of sugar and a little sand, and the 

 mass poured into a narrow tube, say about 5 mm.wide and 20 

 cm. long, the whole being then placed in the incubator and 

 kept at a temperature of about 27 C., an evolution of gas will 

 be observed in about half an hour, and with larger quantities 

 the presence of alcohol can be detected in the usual way. 



This preparation of zymin is termed permanent yeast, 

 because, in contradistinction to the yeast juice of Buchner, it 

 will retain its activity for a prolonged period. Yeast juice, on 

 the other hand, rapidly loses its activity on standing, and such 

 inactive yeast juice is further characterised by the fact that 

 it gives no precipitate on boiling, that is to say, that the 

 albumin content of the juice has been broken down. It would 

 appear, therefore, that in addition to zymase the yeast juice 

 contains another enzyme which is capable of digesting albumin, 

 that is, a proteolytic, or, to use Armstrong's nomenclature, 

 proteoclastic enzyme ; this enzyme would seem to digest not 

 only the albumin present but also the zymase. 



