140 IMPORTANT VARIETIES OF FISSION-FUNGI. 



virulent a form is for a variety of animal, the more cer- 

 tainly it kills without suppuration, the latter being caused 

 only by feebly virulent forms. 



Almost all the diseases enumerated above may be pro- 

 duced experimentally in animals ; the result in experi- 

 mental animals depends very largely upon the virulence 

 and amount of infectious material. 



Also in man streptococci have been successfully inocu- 

 lated (erysipelas, phlegmon). 



Immunity and Immunization. — If an animal resists an injection 

 of the metabolic products, and has after a. time recovered from the 

 consecutive cachexia and loss of weight, then the dose may be increased 

 and gradually a high degree of immunity be obtained. Yet the state- 

 mente of Marmorek are contested, when he claims that horses and asses 

 may thus supply a serum which cures human sepsis ( Petruschky, 

 Schenk). At any rate it has been shown, according to the investiga- 

 tions of Denys and his pupils (C. B. xxiv, 68.5), that the individual 

 varieties of streptococci yield a serum that is active only against the 

 particular variety employed in producing the immunity ; thus also 

 animals, in order to yield serum of therapeutic value, are to be treated 

 with the most variable cultures possible of streptococci ( ' ' polyvalent 

 serum "). Regarding the way in which the serum acts, compare page 

 97. 



Special Methods for Demonstration. — Microscopic 

 form and staining by Gram's method; agar plate in incu- 

 bator; bouillon culture to obtain chains; animal inves- 

 tigation (mouse). 



Forms and Subvarieties of the Strept. Pyogenes. 



All efJorts of authors to characterize sharply the forms 

 of the StrejDt. pyogenes as varieties, subvarieties, or 

 species, and to cover them with names are to be considered 

 as failures. Countless transition forms and the enormous 

 variabilitj' of all the properties make every classification 

 appear insufficient. Even the separation from the Strept. 

 lanceolatus is not always possible. Pasquale (Ziegler's 

 Beitriige, xn, 433), Lemoine (H. R., 1896, 892), Widal 

 and Besan§on (H. R., 1896, 996), and Petruschky (H. R., 

 1897, 772) have all come to analogous results from their 

 minute studies. 



Behring and his pupil v. Lingelsheim arrived at the 

 following usefuP division: 



1 There are found by many authors a "Strept. brevis " without 



