18 BACTERIOLOGY. 



takes place, being much more injurious at high than at 

 low temperature. 



sunlight Sunlight is a very powerful and effective agent 



for destroying bacteria. By experiment it has been 

 proven that the tubercle bacillus, the cause of con- 

 sumption, is killed by sunlight in two hours or less, 

 depending upon the thickness of the material surround- 

 ing it. The effect of electric light and the X-ray 

 is very much less powerful than sunlight, and to be 

 effective must be concentrated and allowed to act for a 

 greater length, of time. 



Heat Heat is the most powerful of all the physical 



agents. Its destructive action is dependent upon the 

 degree of temperature and the length of time it is 

 applied; the higher the temperature, the less the time 

 required. It may be employed either as dry or moist 

 heat. Dry heat is used in the sterilization of glassware, 

 such as flasks, test-tubes, swabs, and pipettes. The 

 temperature should reach 140 to 150 C, and must 

 be allowed to act for one hour in order to effect sterili- 

 zation. The instrument used for this purpose is called 

 a dry-heat sterilizer, and consists of a double-walled 

 box, made of sheet iron and asbestos. An opening in 

 the top admits a thermometer by which the temperature 

 of the inner chamber may be measured. The flame, 

 usually a triple Bunsen burner, generates the heat 

 underneath, which circulates between the walls of the 

 box, keeping the temperature even on all sides. 



For sterilizing all sorts of surgical instruments, 

 except those with cutting edge, moist heat is used. It 



