Conditions Prejudicial to Growth of Bacteria 65 



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\emperature of the cultures being reduced to about 140 

 C., 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* 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. 



The temperature endurance of the molds resembles that 

 of the bacteria. The mycelia are killed at temperatures of 

 60 C. and over, but their spores endure 100 C. The 

 yeasts and oi'dia, that have no resisting spores, are killed at 

 about 60 C. The protozoa are still more sensitive to heat 

 variations than the plant organisms and are killed by less 

 extreme variations. Here again, however, the encysted pro- 

 tozoa endure greater variations than the active organisms. 



Effect of Chemic Agents. The presence of chemic agents, 

 especially certain of the mineral salts, in an otherwise per- 

 fectly suitable medium may completely inhibit the develop- 

 ment of bacteria, and if added to grown cultures in greater 

 concentration, destroy them. Such substances are spoken 

 of as antiseptics in the former, germicides in the latter case. 

 Bichlorid of mercury and carbolic acid are the most familiar 

 examples of germicides. 



Though these agents are supposed to operate in definite 

 concentrations with almost unvarying result, Trambustif 

 found it possible to produce a tolerance to a certain amount 

 of bichlorid of mercury by cultivating Friedlander's bacillus 

 upon culture-media containing gradually increasing amounts 



: "Centralbl. f. Bakt. u. Parasitenk.," etc., May 26, 190x3, Bd. 

 xxvu, Nos. 1 8, 19, p. 684. 



f"Lo Sperimentale," 1893-94. 

 5 



