122 ON VARIABILITY AND ADAPTATION 



in the intensity of virulence of the races of streptococcus. 1 It 

 is interesting to note how, in clinical practice, one observes this 

 conclusion borne out ; to observe the succession of cases passing 

 through ordinary erysipelas and acute lymphangitis, 2 bullous 

 and phlegmonous erysipelas, to acute pyaemia. Indeed, one 

 is driven to the same conclusion with reference to the Strepto- 

 coccus pyogenes that Levy arrived at after several years' work 

 at pyogenic micro-organisms in general. 3 Levy denies that 

 anything can be prognosed from the nature of a microbe causing 

 suppuration. " The prognosis of the process whose origin is 

 referable to a micro-organism depends upon the virulence of 

 the same, and the degree of virulence of pyogenic micro-organisms 

 is subject to extraordinary change." 



It may be that similar changes in virulence will explain the 

 phenomena displayed in the case of swine erysipelas and mouse 

 septicaemia, cholera, and the Odessa fowl disease respectively. 

 The micro-organisms of the first pair of diseases are in appear- 

 ances, size, and method of growth scarce to be distinguished ; 

 but whereas the one form produces a fatal disease in pigs, the 

 other has no action whatsoever upon these animals ; rabbits 

 also are susceptible to swine erysipelas, while they are said not 

 to be affected by mouse septicaemia. Still it is worthy of notice 

 that Loffler has occasionally obtained fatal results in rabbits 

 with inoculations of the bacillus of the latter disease, and that 

 the bacilli of both diseases show themselves peculiarly fatal to 

 white mice, producing similar effects. Quite recently, Lorenz 4 

 has shown that pigs inoculated with cultures of the bacillus of 

 mouse septicaemia are protected against swine erysipelas, and 

 has described a third form, causing an eruptive disease in pigs, 

 which he terms " Backsteinblattern." The bacillus of this, in 

 mode of growth and properties, is intermediate between the 

 other two, and of these three any one, either virulent or properly 

 attenuated, confers immunity against the other two. 



So again with the second pair of diseases. It is impossible 



1 A paper by Behring (Centralblatt f. Bakteriol. xii., 1892, p. 192), just 

 published, confirms this view of the identity of the pathogenic streptococci, 

 and shows that an animal rendered immune to one of the various races 

 of these (vide Lingelsheim, Zeitschrijt f. Hygiene, x., 1891, p. 331 ; gives 

 literature of subject) is now immune to all other pathogenic streptococci. 



2 Vcrneuil and Clado, Comptes rendus, cviii., 1889, p. 7l4. 



3 Levy, Arch. f. exp. Pathol, und Pharmak. xxix., 1891, Parts I. and II. 



4 Lorenz, Archiv f. wiss. u. prakt. Tierheilkunde, xviii., 1892, p. 38. 



