.

This disease is the adynamic pneumonia of the older veterinarians, who
did not recognize any essential difference in its nature from an
ordinary inflammation of the lungs, except in the profound sedation of
the force of the animal affected with it, which is a prominent symptom
from the outset of the disease. Again, this same prostration of the
vital force of the animal, combined with the staggering movement and
want of coordination of the muscles, caused it for a long time to be
confounded with influenza, with which at certain periods it certainly
has a strong analogy of symptoms, but from which, as from sporadic
pneumonia, it can be separated very readily if the case can be followed
throughout its whole course.

Infectious pneumonia is a specific inflammation of the lungs,
accompanied with interstitial edema and inflammation of the tissues of
these organs and a constitutional disturbance and fever. It causes a
profound sedation of the nervous system, which may be so great as to
cause death. It is sometimes attended with pleurisy, inflammation of the
heart or septic complications, which also prove fatal.

Old, cold, damp, foul, unclean, and badly drained and ventilated stables
allow rapid dissemination of the disease to other horses in the same
stable and act as rich reservoirs for preserving the contagion, which
may be retained for over a year.

The virus is but moderately volatile, and in a stable seems rather to
follow the lines of the walls and irregular courses than the direct
currents of air and the tracts of ventilation. Prof. Dieckerhoff found
that the contagion of influenza was readily diffusible throughout an
entire stable and through any opening to other buildings, but he also
found that the contagion of infectious pneumonia is not transmissible at
any great distance, nor is it very diffusible in the atmosphere. A brick
wall 8 feet in height served, in one instance, to prevent the infection
of other animals placed on the opposite side from a horse ill with the
disease, while others placed on the same side and separated from the
focus of contagion only by open bars in the stall were infected and
developed the disease in its typical form.

_Symptoms._--The symptoms differ slightly from those of a frank,
fibrinous pneumonia, but not so much by the introduction of new symptoms
as by the want of or absence of the distinct evidences of local lesions
which are found in the latter disease. All the pneumonias