CHAPTER II 
DISEASES CAUSED BY BACTERIA 
GENUS STREPTOCOCCUS 
General discussion of streptococci. The genus Streptococcus is 
based, according to Migula, on its method of reproduction or division. 
Streptococci are spherical bacteria that divide in one plane. The 
segments do not separate but are held together in short or longer 
chains, although the divisions seem to be complete. Just how the 
segments are held together is not fully determined. According to 
older and more commonly encountered 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 seg- 
ments are oblong and vary in size. Frequently, however, the seg- 
ments vary in size and form in the same chain. 
The more usually observed cultural characters and biochemic 
properties of pathogenic 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 physiological properties and pathogenesis are true 
for different cultures (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 or less influenced by 
its conditions of life. When, for example, two streptococci appear 
to be identical under the majority of tests, a slight deviation 
in a single property cannot be considered of great differential value 
especially if this particular manifestation is among those most subject 
to change. A fundamental difficulty in differentiating species among 
streptococci seems to be a lack of information concerning the possible 
variations brought about by different environments. The further 
difficulty of identifying any of the very large number of forms which 
have been assigned specific names is due to the brevity of their 
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