124 STERILIZATION AND DISINFECTION 
Rubner (1913) has reviewed the application of stcam to sterili- 
zation. He points out that vegetative cells contain much more water 
than spores and thus succumb more quickly to the action of heat. 
Spores contain hygroscopic water which soon evaporates leaving dry 
bacterial protein. This will resist heating for some time. Steam at 
100° C. is an important chemical agent since hydrogen sulphide, 
ammonia and carbon dioxide are liberated from keratin, casein, and 
dried bacteria when they are subjected to its influence. Rubner found 
the saturation of the steam to be about as important as the temperature. 
Steam at 100° C. with a saturation of 80 per cent requires five times 
as long to kill bacteria as does saturated steam and steam with a 
saturation of 70 per cent requires twenty-two times as long as saturated 
steam. If steam at 100° C. is superheated, it is altered in two ways. 
The temperature is raised which makes it a more powerful disinfectant 
and the saturation is lowered which makes it a weaker disinfectant. 
In superheated steam at 110° C. made from steam at 100° C. spores 
lived twice as long and at 127° C. ten times as long. This suggests the 
correlation between the temperature and saturation which are #ery 
important factors in sterilization. According to the laws of disin- 
fection, time is the other factor and it cannot be separated from the 
first two. 
High-pressure Steam. This method has extensive use in bacteri- 
ology. The apparatus is called an autoclave or dressing sterilizer. 
Several types are used, the most convenient of which are connected 
to a steam main from a power plant. Where this is impossible, it may 
be necessary to generate the steam under the sterilizer. This usually 
requires more time since it takes some time to get up the pressure. 
Often it is necessary to keep water in the bottom of the sterilizer in 
order to prevent the superheating of the steam. Under practical 
conditions this is usually not necessary since the steam will be saturated. 
The following table will show the relation between the usual pressures 
and temperatures required for sterilization in the autoclave: 
Temperature, | Temperature, 
Gage Pressure. Gage Pressure. 
Centigrade. Centigrade. 
0 100 15 121 5 
5 109 20 126 
10 115 5 : 40 141 
In the presence of water, Chick has shown that the temperature 
is an important factor in sterilization. The temperature coefficient 
