406 PATHOGENIC MICROORGANISMS 



cause hemolysis and decolorization. It is useful to remember this 

 when examining blood-culture plates, for here the yellow transparent 

 halo of hemolysis and decolorization surrounding the colonies may 

 aid in differentiating these bacteria from pneumococci. This is of 

 especial importance, since many streptococci, when cultivated 

 directly out of the human blood, do not exhibit chain formation, 

 but appear as diplococci. 



In the inulin-serum media of Hiss, 12 streptococci do not produce 

 acid and coagulation. The so-called Streptococcus mucosus, a cap- 

 sule-bearing, inulin-fermenting microorganism, is very probably a 

 sub-species of the pneumococcus (see later section). A very im- 

 portant differential characteristic of the streptococci as a class is 

 the fact that they are not bile soluble. This distinguishes them 

 sharply from the pneumococci. The test is carried out by the 

 method of Neufeld described in the chapter on pneumococci. Ox 

 bile or a ten per cent solution of taurocholate of sodium is added 

 to a young broth culture in proportions of one part of bile or tauro- 

 cholate to nine parts of the culture. 



Resistance. Streptococci on the ordinary culture media, without 

 transplantation and kept at room temperature, usually die out within 

 ten days or two weeks. They may be kept alive for much longer 

 periods by the use of the calcium-carbonate-glucose bouillon, if the 

 cultures are thoroughly shaken and the powdered marble thoroughly 

 mixed with the bouillon from time to time. 13 Preservation at low 

 temperatures (1 to 2 C.), in the ice chest, considerably prolongs 

 the life of cultures. Virulence is preserved longest by frequent 

 transplantation upon albuminous media. In sputum or animal 

 excreta, streptococci may remain alive for several weeks. Strepto- 

 cocci like pneumococci may be preserved alive and with virulence 

 unchanged by drying in the frozen condition by the method 

 described by Swift, and referred to on page 456. For ordinary 

 purposes preservation in tubes of defibrinated rabbit's blood in the 

 ice-chest is the most practical method. 



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

 for ten minutes. 14 Low temperatures, and even freezing, do not 

 destroy some races. 



*- Hiss, Jour. Exp. Me<l v vi, 3005. 



13 Hiss, loe. cit. 



14 Stern'berg, "Textbook of Bact.," 2<1 e<L, 1901; Hartmatni, Arch. f. Hyg., vii. 



