THE PRACTICE OF DISINFECTION 161 



etc., is required, these articles may be passed through 

 the flame. This is the regular method of steriHzing the 

 platinum wire used to transfer bacteria. But, except in 

 an emergency, this method should not be used for 

 surgical instruments, as it destroys the temper of steel 

 and ruins the cutting edge of knives. 

 .- Glassware, such as catheters, pipets, test-tubes, etc., 

 is sterihzed in a hot-air oven. This is a box made of 

 sheet metal with double walls, between which the hot 

 air circulates. It is heated by gas bmners from below, 

 and a temperature of 150° C. for one hour is required 

 to properly steriHze the glass- or metal-ware, for which 

 alone it should be used. The oven of an ordinary kitchen 

 range answers very well for a substitute. (See Fig. 19, 

 p. 44.) 



Chemicals. — ^There are a few objects which cannot 

 be steiiKzed by any of the foregoing methods. Men- 

 tion has already been made of the fact that boihng 

 dulls the edge of knives, which are, therefore, kept in 

 pure carbolic. CHnical thermometers are also kept in a 

 carbolic solution. One of the most difficult materials 

 to render and to keep sterile is catgut, and several ways 

 have been devised for its sterilization. Calgut may be 

 sterihzed by dry heat, being first heated to 70° C. for 

 two hours, to drive off the moisture, '\^^len this has 

 been accomplished the catgut may be exposed to a 

 temperature of 150° C. without becoming brittle. To 

 keep it sterile it is stored in tubes plugged with cotton. 

 A\'hen there is any doubt about its sterility it may be 

 placed for eight days in a 3 per cent, solution of iodin 

 in acetone, then into acetone for four days, to remove the 



excess of iodin, and, finally, into a mixture of acetone 

 11 



