THE STREPTOCOCCUS GROUP 275 



evidence points to streptococci transmitted through milk as the 

 etiological agent. The type of streptococcus involved has been a 

 subject of controversy, but the extensive studies of Smith and Brown 1 

 show clearly that Streptococcus pyogenes is by far the most common 

 organism found. They demonstrated that the streptococcus which 

 is isolated from bovine mastitis is not, except possibly in rare instances, 

 a causative factor in epidemic sore throat. 



Streptococci occur frequently as secondary invaders in diphtheria, 

 many gastro-intestinal diseases, and diseases of the lungs, where they 

 may be at times even more formidable than the primary infecting 

 organism. As Theobald Smith has admirably expressed it, they are 

 ''organisms of the diseased state." The virulence exhibited by strep- 

 tococci varies considerably, as does the type of lesions they excite. This 

 variation in virulence is not at all well understood at the present time, 

 but experiments indicate that the site of infection and the past history 

 of the organism exercise some influence. Rosenow 2 has isolated 

 streptococci, using special methods, from the regional glands in arth- 

 ritis, gall-bladders, and gastric ulcers. He states that the freshly- 

 isolated strains exhibit rather marked tendencies to localize in the 

 homologous tissues of experimental animals. This specific tissue 

 affinity is rapidly lost during cultivation of the organisms in artificial 

 .media, however. 



Animal. Frankel, 3 Petruschky, 4 and Koch and Petruschky 5 showed 

 that the virulence of the same strain of streptococcus varied materially 

 according to the conditions of culture, and that the lesions produced 

 in rabbits varied likewise; thus the descendants of the same culture 

 would produce variously a rapidly fatal septicemia, erysipelas, arth- 

 ritis, endocarditis or peritonitis. Marmorek has shown that the viru- 

 lence of streptococci for animals may be greatly increased by repeated 

 passage; after a series of passages an incredibly small amount of cul- 

 ture, even one one-hundred-millionth of a cubic centimeter of a forty- 

 eight-hour broth culture introduced intraperitoneally may cause death 

 within two days. Streptococci which are virulent for man frequently 

 exhibit but little virulence for animals; it is essential, therefore, 

 that large amounts of material be injected into experimental animals 

 to obtain infection. Rabbits are more susceptible than other labora- 



1 Jour. Med. Research, 1914, xxxi, 455. 



2 Jour. Am. Med. Assn., 1913, Ix, 1223; Ixi, 1947; 1914, Ixiii, 1835. Jour. Inf. Dis., 

 1915, xvi, No. 2. 



3 Cent. f. Bakt., 1889, vi, 671. 



4 Zeit. f. Hyg., 1896, xxiii, 144. 



5 Ibid., p. 478. 



