346 STUDIES ON FERMENTATION. 



the liquid from a flask or vessel containing pure beer in a state 

 of fermentation, and let a few drops of this, with the yeast that 

 it holds in suspension, fall into the flask or can ; the stopper 

 a b is once more passed through the flame and then replaced ; 

 generally in the course of one or two days the jeast develops in 

 the flask sufiicientl}'- for the fermentation to show itself. We 

 may shorten the operation still further by emptying into the 

 can the contents of one of those double-necked flasks. To do 

 this, we have simply to attach the straight tube of the flask to 

 the india-rubber b c, and pour the liquid in. In a similar 

 manner we introduce, through one of the tubulures surmounting 

 the lid of the fermenting apparatus, the contents of the flasks 

 or cans, either whilst they are still in active fermentation, or 

 after fermentation is over. For this purpose, the tap r is con- 

 nected by means of an india-rubber tube (Fig. 79), with a tube 

 passing through a cork fixed in one of the tubulures of the large 

 apparatus. All this may be done in considerably less time than 

 we have taken to describe it ; and the operation may be performed 

 accurately and safely by any one who has witnessed it a few 

 times, even though he may not be skilled in chemical manipula- 

 tions, especiall}^ if he takes care to bear in mind the very simple 

 principles which we have explained. 



Since certain parts of the apparatus — the outer opening of 

 the tap, or the india-rubber tubing, for example — may contract 

 particles of dust from the air, those parts, before being used, 

 must be boiled in water, or washed with boiling water, or 

 passed through the flame of a spirit lamp, to destroy the germs 

 mixed with the particles of dust that settle upon them. 



The method of cooling the wort in contact with carbonic 

 acid prevents access of oxygen to the latter up to the time 

 of pitching, so that the development of the yeast takes place 

 apart from the influence of oxygen. Now, we know that these 

 conditions necessitate the employment of a ver\^ young yeast — 

 a yeast that is in course of active germination, such as may be 

 taken from an incipient preparatory fermentation. Neverthe- 

 less, even with this, the development of the yeast under such 



