SYSTEMATICALLY SELECTED YEASTS. 35 



tioned is of no importance ; practically, we may say we have 

 a sterile liquid. 



The sterilisation of the wort in the large metal vessels 

 (Figs. 5 and 6) is rather more troublesome than is the case with 

 the small glass flasks. I have often heard complaints from 

 pupils who have attended my lectures and exercises, that 

 they could not work at all with these vessels. For this reason 

 I will describe the method in detail. After the vessel has 

 been well cleaned it is charged with about 5 liters of water ; 

 this is then boiled- for an hour, both the tube a and the bent 

 tube remaining open ; the rubber tube at a is then closed by 

 a glass stopper which is first sterilised in the flame, and the 

 boiling is continued for 1 5 minutes during which the steam 

 escapes through the bent tube ; the gas flame is lowered 

 somewhat during this time so that the pressure may not 

 become too great. Shortly before the gas is turned out, 

 the tube b is opened and about 100 cc. of the boiling water 

 run out. In this way the sterilisation of this tube and its 

 contents is secured. It is then closed as before with the 

 pinch-cock and glass stopper; the latter being first rather 

 strongly heated in the flame. The boiling is now finished, 

 and all that remains to be done is to press the cotton-wool 

 filter firmly over the end of the bent tube or to screw on the 

 asbestos filter. Before introducing the wort, the water must, 

 of course, be removed, or at any rate the greater part of it. 

 A mixture of 7 liters of wort with \ liter of water is a suit- 

 able proportion. Sterilisation is effected in the same manner 

 as in the case of the water, but at the end greater precautions 

 are taken. Whilst the 100 cc. of the boiling wort are being 

 withdrawn through the tube b, and during the 15 minutes 

 that the steam is escaping through the bent tube, the latter 

 is strongly heated by means of a second gas flame, and the 

 filter d is then attached with the greatest care. In short, 

 every precaution must be taken that the large bulk of air 

 which is drawn in during the cooling of the wort does not 



D 2 



