FERMENTATION OEGANISMS 103 



enzyme was separated from the broken cells by filtration under 

 great pressure. The drastic methods which Buchner employed 

 are somewhat beyond the facilities of the average student ; 

 nevertheless they should be noted and carried out if possible. 



1. Mis a kUo of brewer's yeast with an equal weight of 

 clean quartz sand and 250 g. of infusorial earth. Put all into a 

 mortar and grind together until plastic and moist. Add 100 cc. 

 of distilled water and transfer the material to a press cloth. 



2. Put the material into a filter press and subject to a pres- 

 sure of 400 or 500 atmospheres. Remove the cake, grind it, add 

 another 100 cc. of water, and press again. Clarify the filtrate 

 obtained by shaking it with fresh infusorial earth and filtering. 



3. Mis 25 cc. of the juice with an equal volume of 10 per cent 

 dextrose solution. Put the solutions into fermentation tubes, 

 with a few drops of toluol added to inliibit bacterial action. Test 

 also cane sugar, levulose, maltose, and lactose. Compare with 

 the results obtained in Exercise 143. 



Exercise 145. The Preparation of an Active Yeast Powder 

 Buchner's yeast juice does not long retain its ability to ferment 

 sugar solutions. A proteolytic enzyme appears to digest not only 

 the protein present but the zymase also. Owing to this fact, as 

 well as to the difficulty of preparation, the yeast juice is not so 

 feasible to study in the ordinary laboratory as the permanent 

 yeast powder (Bauerhefe), or zymin. The preparation of zymin 

 is as follows : 



1. Rub up 500 g. of brewer's yeast, pressed free from most of 

 its water. 



2. Put this yeast into 3 liters of acetone and stir for ten 

 mkiutes. Filter off the acetone, using suction if necessary. 



3. Mix the material with 1 liter of fresh acetone, stir for two 

 minutes, and filter. 



4. Rub up the material with 250 cc. of ether for three minutes, 

 and filter. 



5. Spread the residue on filter paper or porous plates to dry. 

 Keep it at a temperature of 35°-45° C. for twenty-four hours, to 

 drive off ether and acetone. 



