In the laboratory chloroform, H2O2, ether and other volatile or easily decomposable substances have been used to sterilize liquids which could not be treated by heat or by filtration. The agent is removed either by slow evaporation or by exhausting the fluid with an air pump. The method is not very satisfactory, nor is absolute sterilization easily accomplished. It is much better to secure such liquids aseptically where possible.
CHAPTER XV.
DISINFECTION AND STERILIZATION (Continued).
CHOICE OF AGENT.
The choice of the above-described agents depends on the conditions. Evidently a barn is not to be disinfected in the same way that a test-tube in the laboratory is sterilized. Among the factors to be considered in making a choice are the thing to be disinfected or sterilized, its size and nature, that is, whether it will be injured by the process proposed, cost of the agent, especially
when a large amount of material is to be treated. Among the conditions which affect the action of all agents the following should be borne in mind particularly when testing the disinfecting power of chemical agents:
1. The kind of bacterium to be destroyed, since some are more readily killed by a given disinfectant than others, even though no spores are present.
2. The age of the culture. Young bacteria less than twenty-four hours old are usually more readily killed than older ones since the cell wall is more delicate and more easily penetrated, though old growths may be weakened by the accumulation of their products and be more easily destroyed.
3. Presence of spores, since they are much more resistant than the growing cells.
4. Whether the organism is a “good” or “bad” growth, i.e., whether it has grown in a favorable environment and hence is vigorous, or under unfavorable conditions and hence is weak.