96 PHOTO-MICROGRAPHS. 
before using. A drop of the staining fluid is placed 
upon the thin glass cover, to which the organisms 
to be stained are attached, and after a short 
interval is washed away with a gentle stream of 
distilled water, or by agitating the cover, held by 
forceps, in a glass of water. The Bacteria take the 
dye very quickly, and a few seconds will generally 
suffice to stain them deeply with one of the aniline 
colors. 
Methyl violet is generally preferable, as the 
aniline brown stops out the light so completely 
as to destroy any details in the interior of the 
Bacteria, such as granules or endogenous spores. 
Micrococci specifically different from those seen 
in the photo-micrograph under consideration may 
be found in urine which is undergoing the alkaline 
fermentation (Micrococcus ure, Cohn). A variety 
of Bacteria may be found in the stagnant water of 
gutters and small ponds. They may be frequently 
detected as an iridescent film upon the surface of 
the water, and this is readily transferred to a thin 
glass cover by gently bringing the cover, held by 
forceps, in contact with the surface of the water. 
In the same way Bacteria may be picked up 
from the surface of moist mud or from an exposed 
mucous membrane of man or of one of the lower 
animals. Bacteria may also be cultivated espe- 
cially for the purpose by exposing a variety of 
organic infusions to the air. Floating germs fall 
into these, and different species develop in the dif- 
ferent culture-fluids, according as one or the other 
finds the medium most suited for its development. 
