298 



MANUAL OF BACTERIOLOGY. 



that the streptococcus is the cause of scarlet fever, and that 



it seems more likely that this organism is a secondary invader, 



nevertheless the Streptococcus pyo- 

 genes is always present in large 

 numbers in the throats of affected 

 individuals, and causes many serious 

 complications or it may be a fatal 

 termination. Some observers have 

 produced evidence going to show 

 that scarlet fever is caused by strep- 

 tococci. Streptococci are very often 

 found in the pustules of small-pox, 

 and may also appear in the blood. 



The Streptococcus pyogenes is 

 pathogenic for mice and rabbits, but 

 the virulence is very variable. This 

 may sometimes be increased by 

 passing through a number of ani- 

 mals in succession, 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. 



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 

 prepared for combating streptococ- 

 cus infection. These have been 



used in cases of streptococcus infection in human beings; also 



in cases of scarlet fever. 

 Van de Velde, and others have prepared a so-called "polly- 



FiG. 69. — Streptococcus pyo- 

 genes, culture on agar (slightly 

 enlarged). 



