that complete combustion of all fragments occurs before any of the residue (ash) is
removed from the incinerator.
c. Cold. At very low temperatures most microorganisms lose their viability and
multiply very slowly, if at all; but most are not killed. Refrigeration has become an
indispensable adjunct to the food industry, the medical laboratory, and many other
areas in which growth of microorganisms must be inhibited. Some organisms may be
killed at low temperatures--a point of importance in the storage, handling, and shipment
of laboratory specimens. On the other hand, many microorganisms can be frozen for
long periods (as spores) and regain their viability when the temperature is again
d. Desiccation. Natural or artificial drying results in the destruction of most
microorganisms. However, bacterial spores resist drying for long periods. In
dehydrated foods, bacterial growth does not take place; however, microbial action
begins after the foods are reconstituted with water.
e. Radiation. Sunlight and artificially produced ultraviolet radiation have a
germicidal effect on microorganisms. However, neither one is rapid in its effect nor
complete in its action. Both sunlight and ultraviolet lamps are beneficial when used
along with other sound procedures for disinfections. X-rays and other ionizing radiation
are known to be lethal to microorganisms, but their use for this purpose has not been
a. General. Numerous chemical agents are available as germicides,
disinfectants, and antiseptics. Only a few of the principal ones will be discussed here.
Antiseptics and disinfectants may act on microorganisms in anyone of or a combination
of several ways:
Combination with cell proteins to form salts.
Coagulation of proteins
Disruption of the cytoplasmic membrane.
Inhibition or inactivation of enzymes.
b. Phenol. Phenol (carbolic acid) and its derivatives are among the most useful
of the organic germicides. The germicidal efficiency of phenol is used as a standard of
comparison for other antiseptics. A five percent aqueous solution of phenol kills