In the years before the development of the autoclave, liquids and other objects were sterilized by exposure to free flowing steam at 100oC for 30 minutes on each of 3 successive days, with incubation periods between the steaming. The method was called fractional sterilization because a fraction was accomplished on each day. It was also called tydallization after its developer, John Tyndall.
Sterilization by fractional method is achieved by an interesting series of events. During the first day's exposure, steam kills virtually all organisms except bacterial spores, and it stimulates spore to germinate to vegetative cells. During overnight incubation, the cells multiply and are killed on the second day. Again, the material is cooled and the few remaining spores germinate, only to be killed on the third day. Although the method usually results in sterilization, occasions arise when several spores fail to germinate. The method also requires the spores be in a suitable medium for germination, such as a broth.
Importance in modern Age:
Fractional sterilization has assumed renewed importance in modern microbiology with the development of high technology instrumentation and new chemical substances. Often, these materials cannot be sterilized at autoclave temperatures, or by long periods of boiling or baking, or with chemicals. An instrument that generates free flowing steam, such as the Arnold sterilizer, is used in these instances.