64 Biology of Micro-organisms 



when the influenza bacillus of Pfeiffer is inoculated upon 

 blood agar together with Staphylococcus aureus its growth 

 is favored by a change which the staphylococci bring about 

 in the hemoglobin. 



A similar advantageous association has been pointed out 

 by Sanarelli, who found that Bacillus icteroides grows best 

 and retains its vitality longest when grown in company with 

 certain of the molds. 



Rarely, the presence of one species of micro-organism 

 entirely eradicates another. Hankin* found that Micro- 

 coccus ghadialli destroyed the typhoid and colon bacilli, 

 and suggested the use of this coccus to purify waters pol- 

 luted with typhoid. 



An interesting experimental study of the bacterial an- 

 tagonisms with special reference to the Bacillus typhosus, 

 that the student should read, is by W. D. Frost, and appears 

 in the " Journal of Infectious Diseases," 1904, i, p. 599. 



Temperature. According to Frankel, bacteria will rarely 

 grow below 16 and above 40 C., but Fliigge has shown that 

 Bacillus subtilis will grow very slowly at 6 C.; at 12.5 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 30 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 

 (6o-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 

 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. Some adult bacteria and most spores 

 seem capable of resisting almost any degree of cold. Ravenel % 



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



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



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



