Methods of Sterilization 



159 



ology. Before sterilizing, flasks and tubes are therefore 

 carefully plugged with ordinary (non-absorbent) cotton- wool ; 

 they will then remain free from the access of germs until 

 opened. Instruments may be sterilized wrapped in cotton, 

 to be opened only when ready for use ; or instruments and 

 rubber goods sterilized by steam can subsequently be 

 wrapped in sterile cotton and kept for use. It is of the 

 utmost importance to carefully protect every sterilized 

 object, in order that the object of the sterilization be not 

 defeated. As the spores of molds falling upon cotton some- 



Fig. 23. Arnold's steam sterilizer (Boston Board of Health form). 



times grow and allow their mycelia to work their way through 

 and drop into the culture-medium. Roux has employed paper 

 caps (Fig. 24) with which the cotton stoppers can be pro- 

 tected from the dust. These are easily made by curling a 

 small square of paper into a "cornucopia," and fastening by 

 turning up the edge or putting in a pin. The paper is placed 

 over the stopper before the sterilization, after which no con- 

 tamination of the cotton can occur. 



II. Sterilization and Protection of Culture Media. 

 As almost all of the culture media contain about 80 per 



