PATHOGENIC BACTERIA. 



247 



fever is caused by streptococci. Streptococci are very often 

 found in the pustules of small-pox, and may also appear in the 

 blood. 



The Streptococcus pyogenes is path- 

 ogenic for mice and rabbits, but the 

 virulence is very variable. That may 

 sometimes be increased by passing 

 through a number of animals in suc- 

 cession, but is rapidly lost in artificial 

 cultures. It is said that the virulence 

 is best maintained when cultures on 

 gelatin, after forty-eight hours' growth, 

 are kept in a cool place, as in the 

 ice-chest. Marmorek has shown that 

 the virulence may be maintained or in- 

 creased by growing it first in a mixture 

 of human blood-serum (or that of the 

 ass or the horse) with bouillon and 

 then inoculating it into the body of a 

 rabbit, alternating these procedures. 

 In this way it is possible to obtain cul- 

 tures of very high virulence. A serum 

 of uncertain value derived from an 

 immunized horse or ass has been 

 prepared by Marmorek for the cure of 

 streptococcus infection. 



A number of other sera have been pre- 

 pared for combating streptococcus in- 

 fection. These have been used in cases 

 of streptococcus infection in human 

 beings; also in cases of scarlet fever. 

 The results appear somewhat encouraging, although still 

 uncertain. 



Fig. 64. — Stiueptococcus 

 pyogenes, cultttre on 

 Agaje (Slightly En- 

 lasged). 



