CHAPTEE XX. 



Bacillus diphtherias Its 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 fol- 

 lowing way: 



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

 serum mixture. (See chapter 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 membrane. 

 Without touching it against anything else rub it care- 

 fully over the surface of one of the serum tubes; with- 

 out 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 scrap- 

 ings 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 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 

 bacillus diphtherice grows much more quickly on the 



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