340 PATHOGENIC ORGANISMS 



thoroughly shaken and the powdered marble thoroughly mixed with 

 the bouillon from time to time.' Preservation at low temperatures 

 (1° to 2° C), in the ice chest, considerably prolongs the life of cul- 

 tures. Virulence is preserved longest by frequent transplantation 

 upon albimiinous media. In sputimi or animal excreta, streptococci 

 may remain alive for several weeks. 



Streptococci are killed by exposure to a temperature of 54° C . for 

 ten minutes.^ Low temperatures, and even freezing, do not destroy some 

 races. 



The action of various chemical disinfectants has been thoroughly 

 investigated by v. Lingelsheim,^ who reports among others the following 

 results: Carbolic acid 1 : 200 kills streptococci in fifteen minutes. In 

 the same time, bichloride of mercury is efficient in a dilution of 1 : 1,500, 

 lysol in a dilution of 1 : 200, peroxide of hydrogen 1 : 35, sulphuric acid 

 1 : 150, and hydrochloric acid 1 : 150. Inhibition is exerted by car- 

 bolic acid 1 : 550, and by bichloride of mercury 1 : 65,000. Exposure 

 to direct sunhght kills streptococci in a few hours. 



Virulence and Pathogenicity. — Different races of pyogenic strepto- 

 cocci show considerable variations in virulence, and there are few organ- 

 isms, pathogenic both for animals and man, which show such peculiari- 

 ties in virulence. The character or severity of the lesion in man gives 

 little evidence as to the virulence of the organism for animals. Such 

 differences are, to a certain extent, dependent upon inherent individual 

 characteristics, but are rather more likely to be the consequences of pre- 

 vious environment or habitat. Prolonged cultivation upon artificial 

 media usually results in the reduction of the virulence of a streptococcus, 

 while an originally low or reduced virulence may often be much en- 

 hanced by repeated passage of the streptococci through animals. It is 

 noteworthy, however, that while the passage of a streptococcus through 

 rabbits will usually enhance its virulence for susceptible animals in 

 general, repeated passages through mice may increase the virulence 

 for these animals only, even occasionally depressing the virulence 

 for rabbits.^ 



Among the domestic animals, those most susceptible to experimental 

 streptococcus infection are white mice and rabbits. Guinea-pigs and 



1 Hiss, loc. cit. 



"Sternberg, "Textbook of Bact.," 2d ed., 1901; Hartmann, Arch. f. Hyg., vii. 

 't). Lingelsheim, "Aetiol. u. Therap. d. Streptoc. Inf.," etc., Beit. z. Exper. 

 Therap., Hft. 1, 1899. 



* Knorr, Zeit. f . Hyg., xiii. 



