STERILE BREAD PASTE. 



65 



the neck of the flask, with its smooth compact end downwards, which 

 adapts itself closely to the smooth inner surface of the neck of the 



Fig. 24. — Aspergillus albas growing on bread paste. 



flask. When such a flask has been sterilised, the firm plug acts as a 

 mechanical filter, allowing free interchange of air between the atmo- 



