42 
PRINCIPLES OF BACTERIOLOGY 
and 160° C. maintained for at least one hour. Remem¬ 
ber that if combustile articles are sterilized in this 
sterilizer, the temperature should not exceed 200° C. 
as cotton is browned at this temperature. 
Moist Heat.— Boiling may be used for the steriliza¬ 
tion of instruments, syringes and other similar objects; 
vegetative forms (not spores) of bacteria may be de¬ 
stroyed by five minutes’ boiling, while in order to de- 
Fig. 5.—Hot-air sterilizer. 
stroy the spores one to two hours’ boiling is sufficient. 
Live steam is the most practical of the methods of heat 
sterilization; while it may be improvised by use of 
almost any simple household makeshifts, such as a 
double steamer, wash boiler or potato steamer, in the 
laboratories it is carried out by means of so-called “Ar¬ 
nold” sterilizer (Fig. 6). This consists of a round or 
rectangular chamber w r ith an outer cylinder well fitting 
over it, both set in a reservoir about 4 inches high, 
