THE EVOLUTION OF INFECTIONS 43 



type of acute nephritis for over fifty years, to make its reappear- 

 ance in 1915 in the trench warfare along the western front. 

 This is a very remarkable history, but until the causative agent 

 is determined we can do no more than suggest that here is a 

 disease which shows itself when man finds himself in a particular 

 environment, dying out when that environment is departed 

 from. As Professor Welch of Johns Hopkins pointed out some 

 years ago in his Huxley lecture, 1 there is evidence that if man 

 can adapt himself to altered environment, so can microbes ; 

 that if man can protect himself against the toxic action of the 

 bacteria with which he is surrounded, so on their part bacteria 

 can protect themselves against man by increasing their virulence 

 and altering their properties according to circumstances. 



It is in this connexion that the recent series of studies by 

 Professor Rosenow upon the elective localization of streptococci 

 are of extraordinary interest. 2 Briefly, by employing deep tubes 

 of fluid culture medium, which permit streptococci to grow at the 

 oxygen tension most favourable to the particular strain, and 

 by inoculating young growths which still retain the final quali- 

 ties impressed upon them by development in particular tissues 

 and localities, he has been able to show that strains obtained 

 from the gall-bladder in cases of cholecystitis, when inoculated 

 intravenously into animals of the laboratory, are peculiarly apt 

 to localize themselves in the walls of the gall-bladder and there 

 set up cholecystitis ; isolated from the joints in man, to set 

 up arthritis, from duodenal ulcers to set up gastric and duodenal 

 ulcers, from multiple neuritis in man to be recovered from the 

 nerve-trunks in the inoculated animal, in myalgia from the 

 muscles. Growth, that is, in a particular tissue in man, endows 

 the streptococcus with an elective affinity for the same tissue 

 in other animals. "With abundant material to work upon, first 

 at the Memorial Institute, Chicago, and later at the Mayo Founda- 

 tion, Rochester, Illinois, injecting various strains of streptococci 

 into animals of the laboratory, and making routine cultures from 

 various tissues, he found that the average incidence of the cocci 

 in or obtained from muscle was 27 ; with cultures from cases of 



1 British Med. Journ., 1902, ii. 1105. In the same year Ainley Walker had 

 made the same suggestion (Journ. of Pathology, viii., 1902, 34). 



2 See more particularly Journal of the American Medical Association, Ixv., 

 1915, p. 1687, and lxvii., 1916, 662; Journal of Infectious Diseases, xix., 1916, 

 Nos. 3 and 4 (September and October); and Journal of Immunology, i., 1916, 363. 



