CHAPTER XX. 



Bacillus diphtherix — Its isolation and cultivation — Morphological and 

 cultural peculiarities — Pathogenic properties — Variations in viru- 

 lence — Pseudo-diphtheria bacilli. 



Feom 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 Lfiffler's blood- 

 serum mixture. (See chapter on Media.) Pass a stout 

 platinum needle, which has been sterilized, into the 

 membrane and twist it around once or twice, or brush 

 it gently over the surface of the membrane. Without 

 touching it against anything else rub it carefully over 

 the surface of one of the serum-tubes ; without steriliz- 

 ing it pass it over the surface of the second, then the 

 third, fourth, and fifth tubes. Place these tubes in the 

 incubator. Then prepare cover-slips from scrapings 

 from the membrane oil the fauces. If the case is one 

 of 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 diph- 

 theria 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 employed, however, insures a dilution in the 

 number of organisms present, and this, in addition to 

 the fact that the blood-serum mixture is a much more 



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