334 BACTERIOLOGY. 



Diphtheria. 



Diagnosis. — It must not be supposed that all cases 

 diagnosed as diphtheria contain the Lsffler bacillus. It 

 may happen that diphtheria-like conditions, due to other 

 org-anisms, will present themselves. This, so-called false 

 diphtheria is frequently due to streptococci; at times, to 

 staphylococci or to various bacilli. A correct diagnosis of 

 true diphtheria, that due to the Lof&er bacillus, can there- 

 fore be made only by the aid of the microscope. Further- 

 more, a case of diphtheria may be a source of danger, even 

 after complete recovery, because of the continued presence 

 of Loffler bacilli in the mouth. It is important, therefore, 

 not only to recognize the disease as early as possible, but 

 also to recognize the time when the infected individual 

 ceases to harbor the bacillus in question. 



In order to carry out a bacteriological diagnosis of 

 diphtheria it is necessary to have some cotton swabs and 

 some tubes of solidified, inclined blood-serum. The swab 

 can be prepared by twisting a little absorbent cotton around 

 the end of a stout wire (2 mm. wide and 14 cm. long). The 

 swabs are placed in plugged test-tubes and sterilized in a 

 dry-heat sterilizer (p. 160). The culture medium, usually 

 employed, is known as Loffler's blood-serum. It is pre- 

 pared according to the directions given in Chapter XIV. 

 If necessary, ordinary blood-serum or even glycerin-agar 

 may be used. 



The sterile swab is thoroughly rubbed over the affected area, 

 and, if possible, a portion of the false membrane should thus be re- 

 moved. The swab is then streaked over the surface of one or two of 

 the sterile, inclined serum tubes. These are then set aside in the 

 incubator at 35-39° for 18-24 hours. The use of a disinfecting solu- 

 tion, previous to the swabbing of the throat, should be avoided. 



A direct microscopical examination can be made by rubbing the 

 swab over one or more cover-glasses. These are then fixed and 

 stained with Loffler's methylene blue (p. 332). As a rule, however, the 

 most satisfactory results will be obtained by examining and staining 

 the colonies that develop on the blood-serum. On this medium, the 

 Loffler bacillus outgrows the other bacteria that may be present, and 



