350 PATHOGENIC BACTERIA.
organism is introduced into a mouse, rabbit, or guinea-
pig, the animal dies in one or two days. Exactly the
same result can be obtained by the introduction of a
piece of the lung-tissue from croupous pneumonia, by
the introduction of some of the rusty sputum, and gener-
ally by the introduction of saliva.
The post-mortem shows that an inflammatory change
has taken place at the point of inoculation, with a fibrin-
ous exudate resembling somewhat that in diphtheria.
At times, and especially in dogs, there may be a little
pus formed. The other appearances are those of a
general disturbance. The spleen is much enlarged, is
firm and red brown. The blood in all the organs contains
large numbers of the bacteria, most of which exhibit a
distinct lanceolate form and have their capsules very
distinct. The disease is a pure septicemia unassociated
with pronounced tissue-changes.
In cases of the kind described the lungs show no pneu-
monic changes. Likewise, if the hypodermic needle
used for injection be plunged through the breast-wall
into the pulmonary tissue, no pneumonia results. Mon-
ti, however, claims to have found that a true character-
istic pneumonia results from the injection of cultures
into the trachea of susceptible animals. This observa-
tion lacks confirmation.
JNot all animals are susceptible. Guinea-pigs, mice,
and rabbits are highly sensitive to the operations of the
organism ; dogs are comparatively immune.
From this brief review of the peculiarities of the pneu-
mococcus it must be obvious that its reputation in pneu-
monia depends more upon the regularity with which it is
found in that disease than upon its capacity to produce a
similar affection in the lower animals.
As in numerous other diseases, we are unable to furnish
an absolute proof of specificity according to the postu-
lates of Koch.
The disease is peculiar in that recovery from it is fol-
lowed either by no immunity or by one of such brief dura-