CHAPTER XX. 



Bacillus dipMheriss—Hs isolation and cultivation— Morpliological and cul- 

 tural pecnliarities— 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 fol- 

 lowing way : 



Have at hand five or six tubes of Loffler'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 second, 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 

 examination 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 diphtherise grows much more quickly on 

 the serum mixture than do other organisms, makes 



