$8 Biology of Micro-organisms 



Rarely, the presence of one species of micro-organism entirely 

 eradicates another. Hankin* found that Micrococcus ghadialli 

 destroyed the typhoid and colon baciUi, and suggested the use of this 

 coccus to purify waters polluted with typhoid. 



An interesting experimental study of the bacterial antagonisms 

 with special reference to Bacillus typhosus, that the student should 

 read, is by W. D. Frost, and appeared in the "Journal of Infectious 

 Diseases," 1904, i, p. 599. 



Temperature. — According to Frankel, bacteria will rarely grow 

 below 16° and above 4o°C., but Fliigge has shown that Bacillus 

 subtiUs will grow very slowly at 6°C.; at i2.5°C. fission does not 

 take place oftener than every four or five hours; at 25°C. fission 

 occurs every three-quarters of an hour, and at 3o°C. about every 

 half-hour. 



The temperature at which micro-organisms grow best is known as 

 the optimum, the lowest temperature at which they continue active 

 as the minimum, the highest that can be endured the maximum. 



A few forms of bacteria grow at very high temperatures (60°- 

 7o°C.), and are described as thermophilic. They are found in 

 manure piles and in hot springs. Tsiklinskyf has described two 

 varieties of Actinomyces and a mold that he cultivated from earth 

 and found able to grow well at 48° to 68°C., though not at all at the 

 temperature of the room. 



Most bacteria are killed by temperatures above 60° to 7S°C., but 

 their spores can resist boiling water for some minutes, though killed 

 by dry heat if exposed to i5o°C. for an hour or to i7S°C. for from 

 five to ten minutes. 



The resistance of low forms of life to low temperatures is most 

 astonishing. Some adult bacteria and most spores seem capable of 

 resisting almost any degree of cold. RavenelJ exposed anthrax 5 

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

 for thirty minutes; typhoid bacilli, for sixty minutes; and Bacillus ■ 

 prodigiosus, for sixty minutes, the temperature of the cultures being 

 reduced to about — i4o°C., yet in no case was the vegetative ca- 

 pability 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 baciUi are 

 frozen, the greater number of them are destroyed, and that sub- ,< 

 sequent development of the frozen cultures takes place from the few 

 surviving organisms. 

 Bacteria usually grow best at the temperature of a comfortably 



* "Brit. Med. Jour.," Aug. 14, 1897, p. 418. 

 t "Russ. Archiv f. Path.," etc., June, 1898, Bd. v. 



I "The Medical News," June 10, 1899. 1 



§ "Centralbl f. Bakt. u. Parasitenk.," etc., May 26, 1900, Bd. xxvii, Nos. 18, 

 19, p. 684. 



