METHODS OF OBSERVING BACTERIA. 91

Rubin-pararosanilin laydrochlorate.
Methylized, ethylized, and benzylized
pararosanilid:

Crystal violet,

Gentian violet,

Victoria blue,

Methyl green,

Auramin.

The rosanilins are more difficult to prepare
than the pararosanilins, and are generally
mixed with them. The pararosanilins
color more sharply than the rosanilins.

4. Amido-azo combinations:

Bismarck brown,
Phenylene brown,
Vesuvin.

5. Chinolin derivatives:

Cyanin. w—-*

B. Naphthalin group.—Magdala red.

The best anilin dyes made at the present time, and
those which have become the standard for all bacterio-
logical work, are made in Germany by Dr. Griibler. In
ordering the stain the name of this manufacturer should
always be specified.

A whole volume could easily be devoted to scientific
staining. Indeed, the technical difficulties encountered
are so great that no explanations can be too thorough to
be useful. The special methods essential for such bac-
teria as have peculiar staining reactions will be given
with the description of the organism. General methods
only will be discussed in this chapter.

Cover-glass Preparations for General Examination.
—The material to be examined must be spread in the
thinnest possible layer upon the surface of a perfectly
clean cover-glass, and dried. Here it may be remarked
that for bacteriological purposes thin covers (No. i) are
generally required, because thick glasses interfere with
the focussing of the oil-immersion lenses, and that cover-