CHAPTER II. 



DISEASES DUE TO STREPTOCOCCI. 



§ i8. General discussion of streptococci. The con- 

 fusion which exists concerning species in this group of bacteria 

 and the variety of antistreptococcic serums on the market, ren- 

 ders a summary of the present knowledge concerning this group 

 of bacteria somewhat desirable. The genus Streptococcus is based, 

 according to Migula, on its method of reproduction or divi- 

 sion. Streptococci are spherical bacteria which divide in one 

 plane. The segments do not separate but are held together in 

 short or longer chains, although the divisions seem to be com- 

 plete. Just how the segments are held together is not fully de- 

 termined. According to older and more commonly encoun- 

 tered classifications, a streptococcus is simply a number of 

 micrococci (spherical bacteria) united in the form of a chain. 

 In some of the supposedly different species the segments are 

 oblong and vary in size. Frequently, however, the segments 

 vary in both size and form in the same chain. 



The more usually observed cultural characters and bio- 

 chemic properties of different streptococci are quite similar, 

 although it is difficult to obtain two cultures that will exactly 

 agree in all of their manifestations when grown on a large 

 number of media. Their disease-producing powers, however, 

 vary within wide limits. While variations in the physio- 

 logical properties and pathogenesis are true for different cul- 

 tures (species?), it has been found that there is a possibility of 

 much variation in the subcultures of the same species. As 

 with certain other bacteria, their virulence is the first to suffer 

 change. In differentiating species, therefore, the fact must 

 not be overlooked, that the existing characters and properties 

 possessed by the streptococcus in hand, may have been more 



