274 STERILIZATION, ANTISEPSIS AND DISINFECTION 
is reached with the atmospheric pressure; a sudden release of pressure 
would cause violent ebullition of fluid, and a wetting or even expul- 
sion of cotton plugs from test-tubes or flasks. 
Pressure, Temperature, 
pounds. Centigrade. 
100.0° 
5 107.7° 
10 115.5° 
15 121.5° 
20 126.5° 
2. Live steam.— Many solutions are injured by temperatures above 
100° C. ]\Iedia containing sugars (particularly bioses) milk and gela- 
tin are partly decomposed by prolonged sterilization in the autoclave.^ 
An exposure to live steam at 100° C. for thirty minutes on each of 
three successive days usually suffices to effect sterilization of these 
media without injury to the constituents of the medium. This 
method of fractional sterilization depends upon the destruction of 
all vegetative cells during the heating process, and the germination 
of spores into vegetative organisms between heatings. It is assumed 
that all viable spores will have germinated before the third exposure to 
heat, but Theobald Smith- has shown that spores of anaerobic bacteria 
may not vegetate within the specified time. This is particularly true 
of milk and media containing fragments of tissue. A fourth exposure 
to heat after two or three days may be required to insure sterilization. 
The Arnold sterilizer is widely used for fractional sterilization with live 
steam. It consists essentially of a double-walled copper chamber 
surmounting a double-bottomed water reservoir, the lower compart- 
ment of which is shallow and contains but little water. A flame applied 
to this shallow reservoir soon generates steam, which rises through a 
central passage to the chamber in which the material to be sterilized is 
placed. Condensed steam flows by gravity to the upper water com- 
partment, and from thence to the lower heated reservoir to replace the 
evaporation. It takes but a few minutes to generate sufficient steam 
to fill the sterilizing chamber. The sterilizing process begins when the 
contents of the sterilizing chamber have reached 100° C. 
3. Fractional Sterilization at temperatures from 60° to 80° C. is fre- 
quently made use of for materials such as blood serum, which would 
be injured by exposure to 100° C. The sterilizing process is repeated 
for an hour daily over a period of five to seven days. The sterilization 
of Loffler's blood serum in a Koch inspissator is carried out at this 
lower temperature. 
4. Boiling Water.— Petri dishes, culture tubes and other apparatus 
containing pathogenic bacteria may be freed from bacteria by boiling 
in water for five minutes. Practically no progressively pathogenic 
1 A better procedure is to sterilize all carbohydrates in aqueous solution, and to 
add the proper amount to nutrient media subsecjuently. Practically no decomposition 
of carbohydrates occurs if this method is followed as a routine. 
2 Jour. Exp. Med., 1898, 3, 647. 
