36 PURE CULTURES OF 



carry with it any living germs into the liquid. The vessels, 

 after being treated as above, have stood for several months 

 without the contents becoming attacked by micro-organisms. 

 Before being used, samples of wort from each vessel must be 

 drawn off at b y and whilst this is done the bent tube is heated 

 in order that the air which passes into the vessel becomes 

 sterilised. 



As far as we can confine ourselves to comparatively small 

 vessels we naturally make use of glass flasks. In spite of 

 the fragility of this material, these vessels possess material 

 advantages since, on account of their transparency, a check 

 can be kept on the liquid within them. If this control is to 

 have any importance the flasks may only be of such a size 

 that every portion of the liquid and its sediment may be 

 well examined from without. This limit is reached with a 

 capacity of 1-2 liters. If the glass flasks are larger than 

 this it may happen that the liquid contains small colonies 

 of different micro-organisms which may escape detection, 

 although of such a size that they would be at once noticed 

 in the smaller flasks. Only when the colonies of the micro- 

 organisms present have attained large proportions will it 

 be possible to detect them in the large flasks ; but under 

 such circumstances we shall also be able to detect them in 

 the samples withdrawn from the metal vessels. A glass 

 vessel of 10 or more liters capacity is, therefore, no more 

 serviceable in this respect than a metal vessel of the same 

 size ; and as the latter is stronger and more convenient to 

 handle, it is naturally to be preferred. 



Having prepared our flasks and vessels of sterilised wort, 

 it is best to set them aside for a time in order that the wort 

 may take up oxygen from the air through the bent tube. It 

 has been found, for instance, in some experiments that the 

 yeast which had been cultivated in aerated wort gave a 

 satisfactory normal result as regards clarification from the 

 commencement, whilst the same yeast which had been grown 



