Navicular disease appears to the author to have been entirely mistaken as regards its treatment. It is administered to as though it consisted in violent and acute inflammation, whereas it is caused by a different process—namely, ulceration. Inflammation excites the whole system, and occurs in strong bodies: ulceration is a diseased condition peculiar to the aged and to the weakly. Navicular disease is, so far as the writer's knowledge extends, unknown in the unbroken animal. It mostly affects the adult or the aged. It is not inflammatory; for the foot, in the first instance, exhibits no heat, and, in the after-stages, never becomes more than warm. Often the warmth is so very slight that practitioners have to adopt a kind of stratagem to determine which is the more hot of the fore feet. A pail of water is brought forward, and sufficient to thoroughly wet both hoofs is thrown over the feet. The parts are then watched; and that which becomes dry the sooner is reasonably considered the warmer hoof of the two.
Moreover, the consequences of this disease are absorption, which it takes years to effect—not deposition, which is accomplished in a few days. The bone lessens in size, sometimes grows thin, till ultimately it may fracture; the tendon loses in substance, and its fibers separate, till at length they may rupture. All internal structures which enter into the composition of the foot grow less and less, till the hoof becomes obviously small or contracted; for it is a law of nature that, in the living creature, the contents should govern the covering: thus the brain controls the skull, the lungs regulate the chest, etc. etc. The horn alone increases; but it is a curious fact that Nature always endeavors to protect the part she allows to suffer from disease: thus in rickets, with children, the bones of the legs frequently curve; but Nature, true to her principles, strives, by extra deposition, to strengthen the parts which threaten to break through weakness.
All tokens declare the navicular disease to be a chronic affection, attended by symptoms of bodily weakness. The accompanying example of the disorder, taken from the body of a horse which was killed for incurable lameness, will illustrate fully this fact.
A MORBID PREPARATION, KINDLY LENT TO THE AUTHOR BY T. W. GOWING, ESQ.
The diseased surface of the navicular bone exposed, and the affected tendon turned back upon the lower part of the os pedis.
In this specimen, the navicular bone occupies its natural situation between the wings of the os pedis. That portion of the tendon which once shared and concealed the disease is turned back upon the sole of the coffin-bone. What does the inspection disclose? Three small holes within the bone, and a few stains of blood, which denote irritation upon the tendon. For, as the disease progresses, synovia ceases to be secreted, the navicular joint becomes dry, and is subject to the most torturing irritation every time the leg is moved.
That the one presented may not by the reader be supposed an extreme case, produced to support the writer's opinions, another specimen of the disease is given; but, on this last occasion, both sides of the navicular bone shall be exhibited. The upper surface appears perfectly healthy; the lower surface only displays a large clot of blood, and a small but comparatively a deep hole.