DESTRUCTION OF BACTERIA. 19 
is more effective than dry heat, because it has greater 
penetration. Boiling for thirty minutes will destroy 
all forms of pathogenic bacteria and their spores. 
The destructive action is intensified and the danger 
of rusting avoided if sodium carbonate is added to 
Fig. 3.—Dry heat sterilizer. 
the water in amount sufficient to make a i per cent, 
solution. 
Live steam is employed for sterilizing dressings. 
The instrument most often used is the Arnold steril¬ 
izer, which consists of two metal chambers, one within 
the other, beneath which is a pan containing the water 
to be heated. A flame underneath boils the water and 
generates the steam, which rises to the upper chamber 
and penetrates the contents. The exposure of dress- 
