CHAPTER XX. 



Bacillus dipMheriseIte isolation and cultivation Morphological and cul- 

 tural peculiarities Pathogenic properties Variations in virulence. 



FROM the gray-white deposit on the fauces of a diph- 

 theritic patient prepare a series of cultures in the follow- 

 ing way : 



Have at hand five or six tubes of Loeffler's blood- 

 serum mixture. (See article on Media.) 



Pass a stout platinum needle, which has been steril- 

 ized, into the membrane and twist it around once or 

 twice or brush it gently over the surface of the mem- 

 brane. Without touching it against anything else rub 

 it carefully over the surface of one of the serum tubes ; 

 without sterilizing it pass it over the surface of the sec- 

 ond, then the third, fourth, and fifth tube. Place these 

 tubes in the incubator. Then prepare cover-slips from 

 scrapings from the membrane on the fauces. If the case 

 is true diphtheria the tubes will be ready for examina- 

 tion on the following day. 



The reason that plates are not made in the regular 

 way in this examination is that the bacillus of diphtheria 

 develops much more luxuriantly on the serum mixture, 

 from which plates cannot be made, than it does on the 

 media from which they can be made. The method em- 

 ployed, however, insures a dilution in the number of 

 organisms present, and this, in addition to the fact that 

 the bacillus diphtherice grows much more quickly on 



