282 A MANUAL OF BACTERIOLOGY 



not ferment raffinose and inulin (Smillie). Streptococci 

 may frequently be obtained from the blood in acute 

 rheumatism and are regarded by some as being the 

 .causative organism of this disease (see "Rheu- 

 matism "). 



The different effects produced by streptococci abscess 

 in one case, erysipelas in another, cellulitis or pyaemia in 

 a third are attributable partly to differences in virulence, 

 partly to the site of infection and mode of entrance into 

 the body, partly to real differences existing between 

 different races of streptococci, and partly to the selective 

 affinity of streptococci for particular tissues which has 

 already been referred to (p. 176), which may, however, 

 be attributable to difference of race. 



Streptococci have been described in a number of diseases 

 about which we know little, such as variola, scarlatina 

 (8. scarlatince or conglomerate) , and vaccinia, but in most 

 instances they are probably not causal. Strangles, a 

 disease of horses, is caused by the S. equi. 



Anti-serum. Streptococcal infections are of consider- 

 able importance, and an efficient anti-serum would, 

 therefore, be valuable. For its preparation, the viru- 

 lence of the streptococcus has to be increased by passing 

 it through a series of rabbits, and it is only by growing it 

 in serum media that satisfactory cultures for the inocula- 

 tion of the horses can be prepared. Human serum is the 

 best, but is difficult to obtain ; a mixture of asses' serum 

 and peptone beef -broth comes next. The cultures are 

 grown for about a fortnight and are then inoculated into 

 horses, first killed and then living cultures being used, 

 and after a time the blood acquires anti-microbic proper- 

 ties. It is customary now to make use of a " polyvalent " 

 serum, i.e. one prepared by the injection of many strains 

 of streptococci. Thus Havens found that hsemolytic 

 streptococci can be classified by serological tests into three 



