528 DISEASES OF THE HORSE. 
Causes.—The cause of strangles is infection by direct contact with 
an animal suffering from the disease, or indirectly through contact 
with the discharges from an infected animal, or by means of the 
atmosphere in which an infected animal has been. There are many 
predisposing causes which render some animals much more subject to 
contract the disease than others. Early age, which has given it the 
popular name of colt-ill, offers many more subjects than the later 
periods of life do, for the animal can contract the disease but once, 
and the large majority of adult and old animals have derived an 
immunity from previous attacks. At 3, 4, or 5 years of age the colt, 
which has been at home, safe on a meadow or in a cozy barnyard, far 
from all intercourse with other animals or sources of contagion, is 
first put to work and driven to the market town or county fairs to be 
exposed to an atmosphere or to stables contaminated by other horses 
suffering from disease and serving as infecting agents. If it fails to 
contract it there, it is sold and shipped in foul, undisinfected railway 
cars to dealers’ stables, equally unclean, where it meets many oppor- 
tunities of infection. If it escapes so far, it reaches the time for 
heavier work and daily contact on the streets of towns or large cities, 
with numerous other horses and mules, some of which are sure to be 
the bearers of the germs of this or some other infectious disease, and 
at last it succumbs. 
The period of the eruption of the last permanent teeth, or the end 
of the period of development from the colt to an adult horse, at 
which time the animals usually have a tendency to fatten and be ex- 
cessively full-blooded, also seems to be a predisposing period for the 
contraction of this as well as of the other infectious diseases. 
Thoroughbred colts are very susceptible, and frequently contract 
strangles at a somewhat earlier age than those of more humble origin. 
Mules and asses are much less susceptible and are but rarely affected. 
Other animals are not subject to this disease, but there is a certain 
analogy between it and distemper in dogs. After exposure to infec- 
tion there is a period of incubation of the disease, lasting from two 
to four days, during which the animal enjoys its ordinary health. 
Symptoms.—The horse at first is a little sluggish if used, or when 
placed in its stable is somewhat dejected, paying but moderate atten- 
tion to the various disturbing surroundings. Its appetite issomewhat 
diminished in many cases, while in some cases the animal eats well 
throughout. Thirst is increased, but not a great deal of water is 
taken at one time. If a bucket of water is placed in the manger the 
patient will dip its nose into it and swallow a few mouthfuls, allow- 
ing some of it to drip back and then stop, to return to it in a short 
time. The coat becomes dry and the hairs stand on end. At times 
the horse will have chills of one or the other leg, the fore quarters, 
