Conditions Prejudicial to Growth of Bacteria 45 



Most bacteria are killed by temperatures above 6o-75 

 C., but their spores can resist boiling water for some minutes, 

 though killed by dry heat if exposed to 150 C. for an hour 

 or to 175 C. for from five to ten minutes. 



The resistance of low forms of life to low temperatures is 

 most astonishing. Cold inhibits the growth of all bacteria, 

 and immersion in freezing mixtures destroys many. ^ Some 

 adult bacteria and most spores seem capable of resisting 

 almost any degree of cold. Ravenel * exposed anthrax 

 spores to the action of liquid air for three hours, diphtheria 

 bacilli for thirty minutes, typhoid bacilli for sixty minutes, 

 and Bacillus prodigiosus for sixty minutes, the temperature 

 of the cultures being reduced to about 312 F., yet in no 

 case was the vegetative capability of all of the bacteria 

 destroyed, and when transferred to fresh culture bouillon 

 they grew normally. His researches corroborate those of 

 Pictet and Yung and others. 



To say that bacteria are not injured by cold is a mistake, 

 as Sedgwick and Winslow f have found that when typhoid 

 bacilli are frozen, the greater number of them are destroyed, 

 and that subsequent development of the frozen cultures 

 takes place from the few surviving organisms. 



Bacteria usually grow best at the temperature of a com- 

 fortably heated room (17 C.), and are not affected by its 

 occasional slight variations. Some, chiefly the pathogenic 

 forms, are not cultivable except at the temperature of the 

 body (37 C.); others, like the tubercle bacillus, grow best 

 at a temperature a little above that of the normal body. 



(f) The Presence of Antiseptics, etc. The presence of 

 chemic agents, especially certain of the mineral salts, in 

 an otherwise perfectly suitable medium may completely 

 inhibit the development of bacteria, and if added to grown 

 cultures in greater concentration, destroy them. Such sub- 

 stances are spoken of as antiseptics in the former, germi- 

 cides or disinfectants in the latter case. Bichlorid of mer- 

 cury and carbolic acid are the most familiar examples of 

 germicides. 



Though these agents are supposed to operate in definite 

 concentrations with almost unvarying result, TrambustiJ 



* "The Medical News," June 10, 1899. 



f'Centralbl. f. Bakt. u. Parasitenk.," etc., May 26, 1900, Bd. 

 xxvii, Nos. 18, 19, p. 684. 



{ "Lo Sperimentale," 1893-4. 



