18 
BACTERIOLOGY. 
Sunlight 
Heat 
takes place, being much more injurious at high than at 
low temperature. 
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 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 
