VARIETIES OF STREPTOCOCCI 593 



They associate themselves with the primary cause of the disease and increase its 

 virulence, as may happen, for instance, in influenza, enteric fever, and diphtheria. 

 Streptococci are also found as secondary infections following infection with the 

 pneumococcus, the tubercle bacillus and the bacillus of hospital gangrene. A great 

 many of the complications of scarlet fever are due to a secondary infection with 

 streptococci. 



Streptococci occur in the healthy human subject both on the skin and in 

 those cavities which open on the surface of the body (alimentary canal, nose, 

 and, but rarely, in the vagina). They are present also in the saliva, stools, etc. 



Streptococci are also the cause of certain diseases in the lower animals 

 (Chap. XLII). 



Streptococci are also found widely distributed in the air, soil, well water, 

 etc. [and wherever found they seem always derived directly or indirectly 

 from the animal body ( Andre wes)]. The virulence of the organism appears 

 to be rapidly lost outside the body. 



VARIETIES OF STREPTOCOCCI. 



The large number of pathological conditions to which the streptococci can 

 give origin and its occurrence as a saprophyte in the healthy human tissues 

 have for long attracted the attention of bacteriologists. The question 

 naturally arises as to whether or no the streptococci found under these 

 different conditions are all identical. 



For a time there was a tendency to regard the streptococci as including 

 several species : Fehleisen, for instance, stoutly defended the specificity of 

 the streptococci isolated from cases of erysipelas (Streptococcus erysipelatos) 

 and Rosenbach stated that he could with certainty distinguish streptococci 

 obtained from pus (Streptococcus pyogenes) from Fehleisen 's erysipelococcus. 



But Petruschky showed that the same strain of streptococcus would pro- 

 duce indifferently both in man and in the lower animals such varied clinical 

 conditions as erysipelas, suppuration and septicaemia. 



[Clinical experience also rendered Fehleisen's and Rosenbach's views 

 untenable : in clinical practice a streptococcus from a case of erysipelas can 

 originate a puerperal infection. " One and the same strain of streptococcus 

 may at different stages in its career produce now a rapidly fatal septicaemia, 

 now a spreading erysipelas, now a localized suppuration and now no effect 

 at all " (Andrewes and Horder). " It may therefore be accepted as an 

 established fact that a streptococcal infection may assume different clinical 

 manifestations depending upon the resistance of the person infected and 

 upon the structure of the tissue invaded and that quite independently of the 

 source whence the organism was originally derived " (Besredka).] 



The saprophytic streptococcus which is a normal inhabitant of the [mucous 

 surfaces of the] human body should not be differentiated from the pathogenic 

 streptococcus : its saprophytic character will vanish and its virulence increase 

 under the influence of various determining causes such as traumatism, cold, 

 the ancillary action of other organisms, etc. [Andrewes however is of a 

 contrary opinion and holds that the S. pyogenes should be clearly differen- 

 tiated from the saprophytic streptococci (vide infra).] 



The marked pleomorphism of the streptococcus also led many observers 

 to classify these organisms according to their microscopical appearances ; 

 thus streptococci were divided into S. tenuis, S. brevis, S. longus, etc. But 

 microscopical appearances and cultural characteristics are in the case of the 

 streptococci as in the case of the majority of the bacteria very variable and 

 cannot alone be used as a basis of classification. 



