ON NATURAL RACES 121 



the relatively short period of experiment changes so marked, 

 changes persisting through so many generations or cell multiplica- 

 tions, can be brought about, surely it is not difficult to comprehend 

 changes in the natural world whose action is sufficiently great 

 and is prolonged through a sufficiently long period to produce 

 races of even greater permanency, races which might be termed 

 new species. 



ON NATURAL RACES 



Now apart from these results of experiments we possess 

 already a series of data whose explanation is easiest on the 

 supposition that we are dealing, not with forms that are wholly 

 distinct and of separate origin, but with allied forms and natural 

 races. Perhaps the best example is one that has been extensively 

 discussed. Fehleisen's Streptococcus erysipelatosus, the microbe 

 causing erysipelas, is, in microscopic appearance and in mode 

 of growth, indistinguishable from the streptococcus which can 

 be isolated from many boils and cases of abscess formation. 

 Yet certainly the two micro-organisms differ in pathogenicity, 

 differ in the symptoms they induce when isolated. Are we to 

 say that here we are dealing with two distinct species ? A few 

 years ago all bacteriologists answered this question in the affirma- 

 tive, but now most would reply in the negative, although some, 

 among whom may be included Crookshank, 1 still adhere to 

 the old view. The observations of Eugen Frankel would seem to 

 indicate that truly we are dealing with what are only races. 2 

 Frankel obtained from a case of " universal peritonitis " a pure 

 growth of streptococcus. There could be here no question of 

 erysipelas. Taking some of a fifth culture of this, five months 

 after it had been isolated, he inoculated it into a rabbit's ear 

 and produced an exquisite bullous erysipelas, with streptococci 

 in the lymphatics, identical with human erysipelas. The same 

 inoculated into the peritoneal cavity gave rise to a fibrinous or 

 fibrino-purulent peritonitis. From this it is evident that the 

 difference between erysipelas and pyaemia, in its various forms, 

 depends on mode, and locality, of infection and partly on the 

 quantity of virus, on the individual, and lastly, on differences 



1 Crookshank, International Congress of Hygiene and Demography, 

 August 1891. 



1 Bug. Frankel, Centralbl. f. Bakteriologie, vl, 1889, p. 691. 



