FUNDAMENTAL PRINCIPLES OF DISEASE. 83 
spavins, ringbones, inflammation of the glands of the less vascular 
skin of the extremities, greasy heels, thrush, etc. 
Young horses have inflammation of the membranes lining the air 
passages and digestive tract, while older animals are more subject to 
troubles in the closed serous sacs and in the bones. 
The work to which a horse is put (saddle or harness, speed or 
draft) will influence the predisposition of an animal to inflammatory 
diseases. As in congestion, the functional activity of a part is an 
important factor in localizing this form of disease. Given a group 
of horses exposed to the same draft of cold air or other exciting 
cause of inflammation, the one which has just been eating will be at- 
tacked with an inflammation of the bowels; the one that has just 
been working so as to increase its respiration will have an inflamma- 
tion of the throat, bronchi, or lungs; the one that has just been using 
its feet excessively will have a founder or inflammation of the laminz 
of the feet. 
The direct cause of inflammation is usually an irritant of some 
form. This may be a pathogenic organism—a disease germ—or it 
may be mechanical or chemical, external or internal. Cuts, bruises, 
injuries of any kind, parasites, acids, blisters, heat, cold, secretions, 
‘such as an excess of tears over the cheek or urine on the legs, all 
cause inflammation by direct injury to the part. Strains or wrenches 
of joints, ligaments, and tendons cause trouble by laceration of the 
tissue. 
Inflammations of the internal organs are caused by irritants as 
above, and. by sudden cooling of the surface of the animal, which 
drives the blood to that organ which at the moment is most actively 
supplied with blood. This is called repercussion. A horse which 
has been worked at speed and is breathing rapidly is liable to have 
pneumonia if suddenly chilled, while an animal which has just been 
fed is more liable to have a congestive colic if exposed to the same 
influence, the blood in this case being driven from the exterior to the 
intestines, while in the former it was driven to the lungs. 
Symptoms.—The symptoms of inflammation are, as in congestion, 
change of color, due to an increased supply of blood; swelling, from 
the same cause, with the addition of an effusion into the surrounding 
tissues; heat, owing to the increased combustion in the part; pain, 
due to pressure on the nerves, and altered function. This latter may 
be augmented or diminished, or first one and then the other. In 
addition to the local symptoms, inflammation always produces more 
or less constitutional disturbance or fever. <A splint or small spavin 
will cause so. little fever that it is not appreciable, while a severe 
spavin, an inflamed joint, or a pneumonia may give rise to a marked 
fever. 
86444°—16—3 
