animal and in the
feed in an infected stable for a considerable time and if these are
removed to other localities it may be carried in them. It may be carried
in the clothing of those who have been in attendance on horses suffering
from the disease. The drinking water in troughs and even running water
may hold the virus and be a means of its communication to other animals,
even at a distance.

The studies of Dieckerhoff, in 1881, in regard to the contagion of
influenza were especially interesting. He found that during a local
enzootic, produced by the introduction of infected horses into an
extensive stable otherwise perfectly healthy, the infection took place
in what at first seemed to be a most irregular manner, but which was
shown later to be dependent on the ventilation and currents of air
through the various buildings. His experiments showed that the virus of
influenza is excessively diffusible, and that it will spread rapidly to
the roof of a building and pass by the apertures of ventilation to
others in the neighborhood. The writer has seen cases that have appeared
to spread through a brick wall and attack animals on the opposite side
before others even in the same stable were affected. Brick walls, old
woodwork, and the dirt which is too frequently left about the feed boxes
of a horse stall will hold the contagion for several days, if not weeks,
and communicate it to susceptible animals when placed in the same
locality. On two successive mornings a 4-year-old colt belonging to the
writer stood for about 10 minutes at the open door, fully 40 feet from
the stalls, of a stable in which two cases of influenza had broken out
the day before: in six days the colt developed the disease. On the
morning when the trouble in the colt was recognized it stood in an
infirmary with a dozen horses that were being treated for various
diseases, but was immediately isolated; within one week two-thirds of
the other horses had contracted the disease.

_Symptoms._--After the exposure of a susceptible horse to infection a
period of incubation of from four to seven days elapses, during which
the animal seems in perfect health, before any symptom is visible. When
the symptoms of influenza develop they may be intense, or so moderate as
to occasion but little alarm, but the latter condition frequently
exposes the animal to use and to the danger of the exciting causes of
complications which would not have happened had it been left quietly