DIPHTHERIA BACILLUS. 381 



disinfectants (especially solutions of corrosive subli- 

 mate) to the throat. 



Examination of Cultures. The culture tubes which 

 have been inoculated, as described above, are kept in 

 an incubator at 37 C. for twelve hours, and are then 

 ready for examination. When great haste is required, 

 even five hours will often suffice for a sufficient growth 

 of bacteria for a skilled examiner to decide as to the 

 presence or absence of the bacilli. On inspection it 

 will be seen that the surface of the blood-serum is 

 dotted with numerous colonies, which are just visible. 

 No diagnosis can be made from simple inspection ; if, 

 however, the serum is found to be liquefied or shows 

 other evidences of contamination the examination will 

 probably be unsatisfactory. 



In order to make a microscopical preparation a clean 

 platinum needle is inserted in the tube and quite a 

 large number of colonies are swept with it from the 

 surface of the culture medium, a part being selected 

 where small colonies only are found. A sufficient 

 amount of the bacteria adherent to the needle are 

 washed off in the drop of water previously placed on 

 the cover-glass and smeared over its surface. The 

 bacteria on the glass are then allowed to dry in the 

 air. The cover-glass is then passed quickly through 

 the flame of a Bunsen burner or alcohol lamp, three 

 times in the usual way, covered with a few drops of 

 Loffler's solution of alkaline methylene-blue, and left 

 without heating for ten minutes. It is then rinsed off 

 in clear water, dried, and mounted in balsam. When 

 other methods of staining are desired they are carried 

 out in the proper way. 



In the great majority of cases one of two pictures 



