THE MICROSCOPE IN MEDICINE y4ND SANITATION, n? 



be used with a drop of cedar- oil between the lens and 

 the cover-glass, or the slide, if no cover-glass be used. 

 The Abbe condenser is also a necessity for lighting bac- 

 terial preparations. 



The diagnosis of diphtheria is somewhat more com- 

 plicated than that of tuberculosis and involves cultural 

 as well as microscopical methods. The organism occurs 

 at the back of the throat and material for examination 

 is obtained by rubbing a sterile swab of cotton over the 

 whitish patches which appear on the pharynx and fauces. 

 This swab is then passed over a slanting surface of coag- 

 ulated blood- serum upon which after incubation for six 

 to twelve hours at the body temperature minute pearly 

 colonies of the bacilli will appear. A portion of the 

 growth is then removed with a sterile loop of platinum 

 wire and spread over a clean cover-slip in a drop of 

 water. The cover thus prepared is dried, fixed by pass- 

 ing three times through the flame, and stained for ten 

 minutes with Loeffler's methylene blue (30 cc. of a 

 saturated alcoholic solution of the dye mixed with 100 cc. 

 of a Vio.ooo aqueous solution of caustic potash). After 

 washing, drying, and mounting in balsam, the speci- 

 men, in cases of diphtheria, will show the very variable 

 rods characteristic of the diphtheria bacillus, many of 

 them cigar-shaped or club-shaped, and often exhibiting 

 the peculiar cross-barred appearance indicated in Fig. 

 46. Sometimes these organisms will be seen mixed 

 with spherical bacteria arranged in pairs and chains, 

 the streptococci. In negative cultures only cocci are 

 found, as a rule, although other baciUi, more or less 



