472 MUSGRAVE, CLEGG, AND POLK. 



forms of S. caprce described by Silberschmidt are forms of the pure 

 vulture and not bacterial contamination. As to Vincent's case, the 

 organism is distinctive and can not possibly be included in Wright's 

 definition of Actinomyces; indeed, it forms one end of the Streptothrix 

 group, while the Actinomyces of Wright forms the other. 



SPECIES DETERMINATION. 



Species determination in this genus is made extremely difficult, and 

 classification of all the forms which have been given in the literature 

 is impossible, because of the incomplete and imperfect descriptions which 

 are given. Several of these descriptions are old, have not been repeated 

 or confirmed, and are lacking in the elucidation of important points 

 which are now recognized as essential for diagnosis. Our correspondence 

 has elicited the fact that cultures of several of these species are no 

 longer obtainable, and therefore, no further study of them can be made. 

 Fortunately, we have been able to secure cultures of the most important 

 members of the group and by comparative morphologic and biologic- 

 studies, particularly with reference to their pathogenic character, we 

 have been able somewhat to simplify the classification by showing that 

 some of the described species are identical. This includes S. freeri, 

 which from a study of the literature we thought to be a new species, 

 but after comparative study found to be identical with 8. eppingeri in 

 all essential particulars. 



Another difficulty in establishing species or varieties is encountered 

 in attempting to fix the amount of variation necessary to constitute 

 a new species. The differences between various members of the group 

 are practically in every instances those of degree only. For example ; 

 in the requirements for oxygen we have variations from facultative anaero- 

 bism with strong tendencies toward being negative to ox] r gen, as exempli- 

 fied by the Wolf, Israel and Wright type of Actinomyces, to facultative 

 aerobism with strong oxygen requirements, as exemplified in S. eppingeri; 

 while other strains show intermediate stages of aerobiosis. Although 

 strict anaerobes and equally strict aerobes have been mentioned, the con- 

 clusions probably are based upon errors in technique. Certainly this is 

 true with the organisms with which we have worked, for in no instance 

 have we encountered either a strict anaerobic, or an equally strict aerobic 

 Streptothrix, although some of the cultures under our hands have had 

 such properties ascribed to them by others.' 



Staining reactions. — The terminal filaments in lesions and young cul- 

 tures usually stain very well by the usual aniline dyes, but in older 

 colonies the central detritus does not stain and the filaments give irregular 

 staining reactions often showing irregular, including coccus- and ba- 

 cillus-like, forms. The reaction to Gram's solution is somewhat varia- 

 ble, depending upon the age of the colonies and there is some variation 



