CHAPTER V 
STERILIZATION AND DISINFECTION 
BacTeRiA do not exist in nature as pure cultures. Since there are so 
many varieties, the bacteriologist must use media and apparatus which 
are free from not only bacteria but all forms of life. This is accom- 
plished by sterilization, which is to be distinguished from disinfection— 
the removal of pathogenic bacteria only. The methods for sterilization 
may be classified as follows: 
I. Dry heat: 
a. Flaming and incineration. 
.b. Hot air oven. 
II. Moist heat: 
a. Inspissator. 
b. Streaming steam in the Arnold. 
c. High pressure steam in the autoclave. 
d. Boiling. 
III. Filtration: 
a. Through liquids. 
1. Sodium hydroxide, sulphuric acid, ete. 
b. Through solids. 
1. Sand, cotton, glass wool, porcelain, etc. 
IV. Light: 
a. Sunlight. 
b. Ultraviolet. 
Dry Heat 
Death by drying may be the result of two processes. The cell 
protoplasm may decompose or oxidation may take place. This has been 
studied by Paul (1909) and his co-workers who found, in general, that 
the rate of death in dry heat is proportional to the oxygen concentration. 
This would seem to indicate that death in dry heat was an oxidation 
process, although other reactions may enter. With regard to moist 
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