BIOLOGICAL PROPERTIES 599 



[Blood-agar. Schottmiiller used a medium consisting of 2 parts of sterile 

 human blood mixed with 5 parts of ordinary agar. 



[By the characteristics of the growth on this medium, Schottmiiller considered 

 that streptococci could be divided into three groups. 



[I. Streptococcus pyogenes vel erysipelatos which is a long-chained form giving 

 rise to greyish colonies and hsemolyzing the blood. 



[2. Streptococcus mitior vel viridans growing in short chains and giving origin to 

 greenish colonies but producing very slight haemolysis. 



[3. Streptococcus mucosus consisting of capsulated organisms and giving rise to 

 colonies of a mucous, slimy consistency. ] 



Coagulated serum. The colonies are more often discrete otherwise the 

 growth is the same as on agar. 



Marmorek recommends agar over which a drop or two of human serum has 

 been run. 



[Serum-agar. To obtain large quantities of growth for immunizing horses, Bes- 

 redka uses Roux's bottles 22 x 11 cm. and sows on agar which is watered 1 hour 

 before sowing with 1-1 -5 c.c. of heated horse serum (56 C. for | hour).] 



Potato. No growth apparent to the naked eye takes place on potato though 

 if the surface of the medium be scraped and the scrapings examined under the 

 microscope it is evident that some multiplication has taken place. The 

 chains are always short. Marot has described a streptococcus giving rise 

 on this medium to small discrete whitish colonies visible to the naked eye. 



SECTION HI. BIOLOGICAL PROPERTIES. 

 1. Vitality. Virulence. 



Vitality. Under aerobic conditions, streptococci soon die out in artificial 

 culture. Cultures more than a fortnight old often fail when resown. 



When sub-cultivated from agar to agar the organism soon dies out, but in 

 broth sub-cultures can be maintained for a much longer time. Marmorek's 

 [and Besredka's] serum media are better for keeping the organism alive. 

 Sub-cultures from agar can often be obtained by sowing in serum-broth when 

 they fail on ordinary media. Meyer and Ruppel kept streptococci in human 

 blood sealed up in tubes in the ice chest and found that they retained both 

 their vitality and virulence for years. 



In culture, streptococci are readily destroyed. A temperature of 52 C. 

 for 1 hour or 100 C. for an instant suffices to kill the organisms. Antiseptics, 

 even the weakest, are powerfully bactericidal ; chloroform vapour, for 

 example, sterilizes cultures of streptococci almost at once. 



In pus, especially when dried, the organism is more resistant. A tem- 

 perature of 100 C. for a few minutes kills it but it will resist ordinary anti- 

 septics for a fairly long time. 



[Some of the non-pathogenic forms of streptococci the S. equinus of Andrewes and 

 Horder (vide infra) are highly resistant and will withstand drying on garnets for several 

 months. ] 



Virulence. Streptococci soon lose their virulence when grown on the 

 ordinary culture media, but the virulence may be maintained by keeping the 

 organism under anaerobic conditions or in broth containing calcium carbonate 

 or, more certainly still, in human blood or in the serum media of Marmorek 

 [and Besredka]. The virulence is not raised by sub-culturing in the latter 

 media but is maintained for several generations. 



Streptococci isolated from human lesions (suppurative lesions, sore throats, 

 septicaemias, etc.) are, as .a rule, very slightly virulent for the lower animals 

 and may even be totally non- virulent for rabbits and mice : Vei lion's Strepto- 

 coccus tennis and von Lingelsheim's Streptococcus brevis are examples of the 



