Page 84 - My FlipBook

58 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

test tabes placed obliquely, so as to obtain the greatest possible
surfiice. Only line or puncture cultures can be made with this
material ; it is particularly adapted to the cultivation of the
tubercle bacillus, the bacillus of glanders, and some other patho-
genic micro-organisms.
Boiled potato is a medium of great value in the determina-
tion of bacteria. No medium, however, requires greater care in
preparation and after-treatment than this, in order to obtain sat-
isfactory results. Any sound potato which (Joes not become mealy,
or crdck open on boiling, will do for the purpose ; it is first thor-
oughly washed and brushed, and all defective spots and deep eyes
being removed, it is placed for one hour in a 5 to 1000 solution of
bichloride of mercury, then in a steam sterilizer for one-half an
hour to one hour. In the mean time the damp chamber is sterilized,
and the bottom lined with filter-paper wet with sublimate solu-
tion, 5 to 1000. The potatoes are, while hot, removed from the
sterilizer with sterilized forceps, cut into halves with a cold ster-
ilized knife, and placed directly upon the sublimate paper (the
cut surface up) and the cell closed. Potato sections prepared in
this way should remain unchanged indefinitely. When the potato
has become cool, the cover of the cell is carefully removed, and
the micro-organism which is to be cultivated is spread upon a
space about as large as a dime, in the center of the section. Micro-
organisms which morphologically, as well as in their reaction
upon gelatine, agar-agar, and blood-serum, show no appreciable
diiierences, may sometimes be easily distinguished by aid of the
potato culture. The potato can seldom be used to prepare
pure cultures. It is chiefly used as a reagent in distinguishing-
between growths already in pure culture. For example, all
comma bacilli yet discovered grow on potato, except the one
found by Deneke in old cheese, w^hich does not develop at all
on potato, and is thereby at once distinguished as an entirely
difierent bacterium.
Eggs may often be used to great advantage. They are pre-
pared as follows : The fresh egg is placed in sublimate, 5 to 1000,.
for ten minutes, then in the steam sterilizer for one hour. The
cell for eggs is prepared as for potatoes, except that a sterilized
glass plate, resting on a glass bench, is placed in the bottom to-