INFECTIOUS DISEASES. 581 
rapidly, and if urged to go faster may sustain a fracture or have a 
ligament torn from its bony attachments, especially in the lower 
bones of the leg. An affected horse weighing 1,000 pounds was seen 
by the writer to fracture the large pastern bone from rearing during 
halter exercise. 
The animal becomes poor in flesh, the coat is rough and lusterless, 
and the skin tight and harsh, producing a condition termed “ hide- 
bound,” with considerable “ tucking up” of the abdomen. The horse 
shows a short, stilted, choppy gait, which later becomes stiffer and 
more restricted, while on standing a position simulating that in 
founder is assumed, with a noticeable drop to the croup. The animal 
at this stage usually lies down and remains recumbent for several 
days at a time. Bed sores frequently arise and fractures are not 
mcommon in consequence of attempts to arise, which complications, 
in addition to emaciation, result in death. 
The disease may exist in this manner for variable periods extend- 
ing from two or three months to two years. The termination of the 
disease is uncertain at best, but is likely to be favorable if treatment 
and a change of feed, water, and location is adopted in the early 
stages of the malady. 
Lesions.—As has been stated, the bones are the principal tissues 
involved. The nutrition of the bone is disturbed, as is indicated by 
the diminished density or rarefaction of the bony substances, the 
increase in the size or widening of the Haversian canal and the 
medullary cavity, and the enlargement of the network of spaces in 
the spongy tissue, the absorptive changes following the course of the 
Haversian system. In this process of absorption there are formed 
within the substance of the bone areas of erosion, indentations, or 
hollow spaces of irregular shape. These spaces increase in size and 
become confluent, causing an appearance resembling some varieties 
of coral. The affected bone may be readily incised with a knife, the 
cut surface appearing finely porous. This porous area is soft, pli- 
able, and yields easily to the pressure of the finger. It has been 
shown by chemical analysis that the bone of an osteoporotic horse, 
when compared with that of a normal horse, shows a reduction in 
the amount of fat, phosphoric acid, lime, and soda, but a slight in- 
crease in organic matter and silicic acid. The bones lose their yel- 
lowish-white appearance, becoming gray and brittle. The affected 
bones may be those of any region or portion of the body. Besides 
the change already noted in the bones of the face, the ends of the 
long bones, such as the ribs, are involved, and may be sectioned, 
though not so readily as the facial bones. The bones of the vertebra 
are also frequently involved, necessitating great care in casting a 
horse, as the writer has seen several cases of broken backs in casting 
such animals for other operations. The marrow and cancellated 
