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 
