2 Scientific Proceedings^ Royal Dublin Society. 



fermentation of the wort is almost complete. From this the beer is removed 

 by centrifuging, or by pressing through a fine liuen cloth. The yeast, then a 

 plastic mass, is made up into cylinders 10-15 em. long, and 1"5 cm. diameter, 

 and wrapped in paper. In this form it is lowered by means of a thread into a 

 Dewar flask containing liquid air.' It is left immersed for ten or fifteen minutes 

 till the cessation of active ebullition of the air indicates that the mass has fallen 

 to the temperature of the liquid air. The cylinder is then withdrawn from the 

 flask, the paper is removed from its lower end, and it is transferred to the 

 tube of the centrifuge. As it thaws, the yeast runs down out of its paper 

 covering into the tube. It is remarkable that the yeast, which before the 

 application of liquid air was a sticky, plastic mass, has now, after exposure to 

 the intense cold, become quite fluid. This change of consistency is observed 

 even when condensation of atmospheric moisture on the cold and thawing 

 mass is precluded. 



Centrifuging for ten minutes, at 9000 revolutions per minute, causes the 

 yeast-cells to sink in this fluid mass, and to leave a faintly opalescent brown 

 liquid above. The volume of this liquid is about 30 per cent, of the volume of 

 the plastic yeast frozen, and represents the juice or sap of the treated yeast- 

 cells. This liquid has powerful fermentative properties, and contains 

 zymase. 



In one of the first experiments carried out in this manner, we took 160 c.o. 

 of pressed yeast, froze, thawed, and centrifuged it in the manner described, 

 thus obtaining 60 c.c. yeast sap. To 50 c.c. of this, 20 grammes cane-sugar 

 was added, and the mixture was introduced into an Erlenmeyer flask in a 

 thermostat at about 33° C. The flask was connected by means of a rubber 

 tube leading out of the thermostat to two gas-burettes connected in series. 

 The CO2 evolved displaced mercury from the first burette into the second. 

 When reading the volume, the mercury in the two was adjusted so as to 

 stand at the same level. This arrangement, which was found quite convenient, 

 was adopted in all the experiments. 



Before each reading the fermenting fluid was thoroughly shaken. 



1 As in our previous work, we are indebted to Professor W. H. Thompson for the li(iuid air used 

 in these experiments. 



