356 EXPERIMENTS ON PLEURO-PNEUMONIA. 
death. The internal organs, and in particular the lungs, were 
found to be perfectly healthy; but the serous membranes ex¬ 
hibited the appearances ordinarily observed in animals that 
have died of acute general infection, that is, from what is 
popularly called blood-poisoning. 
In the cases I have related the effects of inoculation were, 
as has been seen, severe in every instance; for even in the 
three animals that recovered, the disturbance of health, as 
indicated by the high temperature and general state of the 
animal, was considerable. When the tail is selected as the 
seat of inoculation the case is much more manageable. Here, 
as before, it is not until the fourth or fifth day that the seat 
of puncture becomes painful and swollen. The swelling con¬ 
tinues for about a week, by which time a slough of dead tissue 
has usually formed, which eventually separates. About the 
time that the slough comes away secondary swelling usually 
begins, and gradually extends to a greater or less distance to¬ 
wards the root of the tail, until, in favorable cases, the neigh¬ 
bouring integument is involved, becoming the seat of diffuse 
cellular infiltration of the same kind as that which has already 
been described. In the ordinary case, a common result of 
tail inoculation is that part of the organ separated by necrosis, 
an event which is often not attended with any serious dis¬ 
turbance of the animal’s health. 
There are two reasons why inoculation, as practised in the 
above instances, is necessarily attended with danger. One of 
these is that the liquid used, however carefully it is collected, 
not only contains the virus of pleuro-pneumonia, but possesses 
morbific properties of another kind, which are due to its being 
the product of an unhealthy, or, as it is often called, infective 
inflammation—properties which would have manifested them¬ 
selves if, instead of the juice of a pleuro-pneumonia lung, we 
had used any other exudation liquid of a similarly infective 
character. A second source of danger is, that the living tissue 
which serves as the channel of introduction is one which we 
know to be particularly susceptible to infective influences of 
this kind. By previous experiments, relating to another 
inquiry, we have found that this second danger could be 
avoided by infusing the morbific liquid directly into the cir¬ 
culation. We therefore resolved to adopt this plan, feeling 
sure that, if the pleuro-pneumonic virus possessed any 
protective power at all, that power would be exercised to the 
greatest advantage if the liquid were mixed with the cir¬ 
culating blood; for in this way it would necessarily come 
into contact, not merely with any particular part but with 
every organ in the body. Another advantage which the 
