STREPTOCOCCUS PYOGENES 343 



those forming the long chains, streptococcus longus, are the 

 only ones concerned in animal pathology, and hence the 

 only ones by which pathogenic powers may be exhibited; 

 while those forming the short chains, streptococcus brems, 

 are not, as a rule, pathogenic, and may often be readily 

 differentiated from the other variety by more or less gross 

 cultural characteristics, such as slow liquefaction of gelatin, 

 visible growth on potato, etc.' 



Antistreptococcus Serum. — Numerous investigators have 

 demonstrated that certain animals — notably horses and 

 asses — as well as some smaller animals, may be rendered 

 immune from streptococcus pyogenes. Further, that in 

 varying degrees the blood serum of such immune animals 

 has both a curative and a prophylactic influence upon the 

 course of streptococcus infection in human beings. 



The method of producing the serum is, in general, to 

 inject gradually increasing doses of virulent streptococcus 

 pyogenes into the tissues of the animal until its blood serum 

 is found to have an inhibiting effect upon experimentally 

 produced streptococcus infection in test animals. 



Reports upon the therapeutic use of antistreptococcus 

 serum in a variety of streptococcus infections are dis- 

 cordant; some authors being enthusiastic as to its curative 

 value, others skeptical or actually denying to it such virtues. 

 The reasons for these divergent opinions are now pretty 

 manifest. It seems well established, from studies of this 

 and other infective organisms, that there are regularly 

 encountered in various pathological processes different 

 strains of one and the same species; strains that, while 



' v. Lingelsheim, Zeitschrift filr Hygiene, 1891, Band x, and 1892, Band 

 xii; Behring, Centralblatt filr Bakteriologie und Parasitfenkunde, 1892, 

 Band xii. 



