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214                 PATHOGENIC BACTERIA.

this is observed, the heating is sufficient, and the temper-
ature can be subsequently maintained by intermittent

If evaporation is allowed to take place, a ring of in-
crustation occurs at the edge of the area covered by the
stain and prevents the proper action of the acid. To
prevent this more stain should now and then be added.
The staining is complete in from three to five minutes,
after which the specimen is washed off with water, the
excess of water absorbed with paper, and 3 per cent,
hydrochloric acid in 70 per cent alcohol, 25 per cent,
aqueous sulphuric, or 33 per cent, aqueous nitric acid
solution dropped upon it for thirty seconds, or until the
red color is just extinguished. The acid is washed off
with water, and the specimen is dried and mounted in
Canada balsam. Nothing will be colored except the tu-
bercle bacilli, which will appear red.

Gabbett modified the staining by adding methylene
blue to the acid solution, which he makes according to
this formula:

Methyl blue,                       2 ;

Sulphuric acid,                  25 ;

Water,                              75.

In Gabbett's method, after staining with carbol-fuch-
sin the specimen is washed with water, acted upon by
the methylene-blue solution for exactly thirty seconds,
washed with water until only a very faint blue remains,
dried, and finally mounted in Canada balsam. By this
method the tubercle bacilli are colored red, and the pus-
corpuscles, epithelial cells, and the unimportant bacteria

The possible relation that the number of bacilli in the
expectoration of consumptives might bear to the progress
or treatment of the case has been elaborately investigated
by Nuttall.1 The total quantity of sputum expectorated
in twenty-four hours was caught in covered, scrupulously

1 Bull, of the Johns Hopkins Hospital, May and June, 1891, ii., 13.