Degenerative atrophy, in hæmoglobinuria, laryngeal hemiplegia,
neurectomy, nerve lesion, brain or cord lesion, lead poisoning,
disuse. Dermatitis, ulceration, morbid secretion, polyuria,
mellituria, albuminuria, poisonous milk.
=Degenerative Atrophy=. From section, disease, atrophy or degeneration
of nerves or nerve centres, the muscles, which they normally innervate,
waste, often to an extreme degree. As examples of this we see the
atrophy of the triceps extensor cruris and other groups in
hæmoglobinuria, of the intrinsic laryngeal muscles in _roaring_, of the
muscles supplied in neurectomy, and of groups of muscles in myelitis,
broken back, lead paralysis, and scapular muscular atrophy. True to the
law of wasting of physiologically inert organs, the nerves are atrophied
and degenerated, and often also the bones, joints and skin.
The degeneration of an active organ applies to the nervous tissues
themselves. According to the law of Waller, the nerve fibre (axis
cylinder), when cut off from its nutritive centre (cell body with
nucleus) degenerates and ultimately perishes. The axis cylinder is a
component part of the neuron, which includes also its continuation in
the cell and nucleus, and when the latter, which is the source and
origin of both nerve impulse and trophic control, is lost, the inactive
axis of the nerve fibre degenerates. This law is now availed of in
tracing the distribution of nerve filaments, the degeneration being
found in those that have been cut off from their nerve cells while those
that come into the nerve trunk from other sources, distal of the injury,
maintain their integrity.
In addition to this peripheral atrophy, a degeneration central of the
injury to the nerve is seen under certain conditions, but especially in
intrauterine life. In such cases the atrophy may extend up to and
include the central nerve cells, causing a secondary central nervous
lesion from an initial peripheral one.
By bearing these laws of nerve atrophy in mind, lesions that would
otherwise be obscure, may be satisfactorily accounted for.
=Eruptions and Ulcerations of Nervous Origin.= Herpes or shingles in man
is now recognized as a nervous disease, circumscribed to the
distribution of given nerves and occurring unilaterally or bilaterally.
Deep-seated dermatitis, vesicles, neuralgia, pain, itching and
formication are common accompaniments. The whole is traced to disease of
the ganglion on the posterior (superior) root of the spinal nerve
distributed to the part. This establishes a principle, and in
inscrutable and obstinate, circumscribed skin disease the veterinarian
should see if it coincides with the distribution of one or more sensory
spinal nerves.
_Ulcerations_ are often caused by the lack of protection of a part after
paralysis, thus perforation of the cornea will follow section or disease
of the trigeminus. These may be prevented by carefully covering the
part, and even cured by a fine protective covering like collodion.
=Alteration of the Secretions= often follow on section of the
sympathetic trunks, that of the cervical sympathetic in rabbits causing
excessive congestion of the facial skin, with exudation and scabby
product, also profuse secretion of sweat, tears, and ear cerumen and
dry, scaly skin.
=Polyuria= is determined by section of one point of the medulla behind
the root of the vagus, _mellituria_ by puncture between the vagus and
auditory nerves (the hepatic vaso-motor centre), and _albuminuria_ by a
puncture in front of the latter. Impairment of the hepatic vaso-motor
tracts in the spinal cord, or of the anterior or posterior cervical
sympathetic ganglia, or of the first thoracic ganglion equally
determines nervous mellituria.
=Poisonous milk= produced in hard worked mares, or over-excited dams of
other species, causing dyspepsia, diarrhœa, arthritis or other trouble
in the suckling, must be in part attributed to nervous disorder.
Practically all secretions and nutrition are largely under nervous
control, so that modifications in quantity or quality can often be
attributed to nervous influence.