204 Sterilization and Disinfection 



In sterilizing the wires attention must be bestowed upon 

 the glass handle, which should be flamed for at least half 

 its length for a few moments when used for the first time 

 each day. Carelessness in this respect may result in the 

 contamination of the cultures. 



Knives, scissors, and forceps may be exposed for a very 

 brief time to the direct flame, but as this affects the temper 

 of the steel when continued too long, they are better boiled, 

 steamed, or carbolized. 



All articles of glassware are to be sterilized by an exposure 

 of one-half to one hour to a sufficiently high temperature 

 150 C. or 302 F. in an appropriate hot-air oven. This 

 temperature is fatal to all forms of microscopic life. 



Rubber stoppers, corks, wooden apparatus, and other 

 objects which are warped, cracked, charred, or melted 

 by so high a temperature must be sterilized by exposure to 

 streaming steam or steam under pressure, in the steam 

 sterilizer or autoclave, before they can be pronounced 

 sterile. 



It must always be borne in mind that after sterilization 

 has been accomplished the original sources of contamination 

 are still present, so that it is necessary to protect the sterilized 

 objects and media from them. 



To Schroder and Van Dusch belongs the credit of having 

 first shown that when the mouths of flasks and tubes are 

 closed with plugs of sterile cotton no germs can filter through. 

 This discovery has been of inestimable value, and has been 

 one of the chief means permitting the advance of bacteri- 

 ology. If, before sterilizing, flasks and tubes are carefully 

 plugged with ordinary (non-absorbent) cotton-wool, they and 

 their contents will 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- 

 times grow and allow their mycelia to work their way 

 through and drop into the culture-medium. Roux has em- 

 ployed paper caps, with which the cotton stoppers can be 

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

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



