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276                 PATHOGENIC BACTERIA.

great majority of the spores except those of tetanus, were
destroyed, and, as little other than tetanus spores re-
mained, their cultivation was made comparatively easy.
The resistance which the tetanus bacilli manifest toward
heat is only part of a great general resisting power of
which they are possessed. It is said that they can retain
their vitality in the dried condition for months. Stern-
berg says they can resist 5 per cent, carbolic solutions
for ten hours, but will not grow after fifteen hours' im-
mersion. 5 per cent, carbolic acid, to which o. 5 per cent.

FIG. 75.—Bacillus tetani: five-days-old colony upon gelatin containing glucose;
x 1000 (Frankel and Pfeiffer).

of hydrochloric acid has been added, destroys them in
two hours. They are also destroyed in three hours by
i: 1000 bichlorid-of-mercury solution ; but when to such
a solution o. 5 per cent, of hydrochloric acid is added, its
activity is so increased that the spores are destroyed in
thirty minutes. The resistance to heat is only within
certain limits, for exposure to passing steam for from
five to eight minutes is certain to kill the spores.
The colonies of the tetanus bacillus, when grown in