STUDIES OX FERMENTATION. 345 



with glass tubes (Fig. 78). The vessel must be half or two-thirds 

 filled with wort. For this purpose it will be well always to em- 

 ploy wort that has been preserved in bottles by Appert's process. 

 We must use a stopper provided with tubes, as represented in 

 Fig. 79 : a bis a, glass stopper which closes the india-rubber tube 

 be; mnp is a fine glass tube, or, better still, made of copper. 



The tap r being closed, a long india-rubber tube is attached 

 to the extremity of the curved tube, and the flask is completely 

 immersed in a hot-water bath ; the india-rubber tube projects 

 from the bath and keeps the interior of the vessel in commu- 

 nication with the external atmosphere. If the tube m np is of 

 copper, we may avail ourselves of its flexibility and bend it 

 upwards, so as to place its open extremity outside the bath. 

 The water in the bath is then gradually raised to a temperature 

 of 100° C. (212° F.), at which it is kept for a quarter or half an 

 hour. In the case of copper cans, it is more convenient to 

 place them over a gas-heater. They may be treated in the 

 same manner as the flasks with curved necks. Vessels pre- 

 pared in this manner may remain in a laboratory, or in any 

 part of a brewery, for an indefinite time, without the wort in 

 them undergoing the least change. It gradually darkens in 

 colour through a direct oxidation of a purely chemical nature, 

 but no tendency to disease will manifest itself. 



Some days before we require to pitch an apparatus of several 

 hectolitres, we impregnate one of these flasks or cans.* For 

 this purpose we pass the flame of a spirit lamp over the tubes 

 a b a and m np, to destroy the particles of dust that might pass 

 inside at the moment when the stopper a h is taken out, and 

 then by means of a long, straight glass tube we take some of 



* As stated in the paragrapli on aerobian ferments, in Chapter V., 

 "low" yeasts, to be preserved in their state of " lowness," must be 

 submitted to often-repeated growths — every fifteen days in winter and 

 every ten days in summer, that is to say, they must be grown afresh after 

 each of these intervals. If this is done, there will be no reason to appre- 

 hend the formation of aerobian ferments, which, as we have stated 

 before, may embarrass us by transforming our " low " yeasts into " high " 

 yeasts. 



