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METHODS OF BACTERIOLOGICAL INVESTIGATION. 49
on boiling with water yield a jelly that solidifies at temperatures
above that of the human body.
Platinum needle : a piece of platinum wire, about two and one-
half inches long, with one end melted into the end of a glass.
rod (Fig. 12).
Fig. 12.

Platinum Needles.
Damp chamber : a shallow glass vessel whose bottom is cov-
ered by a piece of wet bibulous paper, and over which a second
somewhat larger vessel is inverted (Fig. 13, b) ; or the arrange-
ment illustrated in Fig. 13, a, may be used. Damp chambers
may, how^ever, be constructed of almost any two vessels,—for
example, of two soup-plates.
Colony : a cryptogamous growth on the surface of, or within
a layer of solid nutritive material, proceeding from one cell and

Fig. 13 a. Fig. 13 h.

Damp Chambers.

consisting of a number of cells, varying from a few to myriads.
The larger colonies are plainly visible to the naked eye, and
their color, form, structure, densit}^, etc., furnish a ready means
for distinguishing between different kinds of micro-organisms
without the aid of the microscope, or often when even the
microscope fails to furnish the necessary information.

Apparatus.
The accessories absolutely necessary for beginning work in
bacteriology are very few and inexpensive. I began work with
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