36 



MICRO-ORGANISMS AND FERMENTATION. 



in the application of 0-036 per cent., after which the milk is 

 maintained for three hours at 50 to 52C. 



5. Flasks. 



All vessels in which cultures are made mustjsatisfy the 

 condition that they are proof to every contamination from 

 without. Pasteur flasks satisfy this demand in the highest 

 degree. The illustration (Fig. 5) shows this flask in the 

 improved form employed in the Carlsberg Physiological 

 Laboratory. When the hopped wort (preferably filter-bag 

 v ort) is boiled, the steam first escapes through the straight 

 t ibe, attached to which is a short piece of rubber tubing ; 



Via. 5. Pasteur's tin 



i^'. (i. -Chamberltnd flask. 



when this is closed (after boiling for about half an hour) 

 the only outlet for steam is through the bent tube. 

 About twenty minutes later, the flask is removed from the 

 sand-bath. During cooling the germs are deposited in the 

 lowest part of the bent tube, or are not carried beyond the 

 enlargement of the tube, and, therefore, do not come into 

 contact with the liquid. Hence, it is evident that the lower 

 part of the bent tube must be heated whenever the flask is 

 to be agitated or emptied through the straight tube. If the 

 fiask is to be opened and connected with another flask, this 

 must be effected either in a small sterile space, or else the 

 opening and connecting must be carried out in a flame. A 

 Bunsen burner is placed directly in front of the operator. 



