Hyperæsthesia, cutaneous, thermic, muscular, visceral. Paræsthesia,
pressure on nerve. Anæsthesia, partial, drug. Analgesia. Hyperalgesia.
These are necessarily much less obvious to the veterinarian than to the
physician of man. Yet in certain cases they may be observed directly,
and in others deduced from dependent symptoms.
=Hyperæsthesia= is a state of exalted excitability of any part of the
sensory nervous apparatus.
=Cutaneous hyperæsthesia= is that condition in which the slightest touch
gives rise to an instant and extreme response. Some nervously organized
mares which are dangerously ticklish and irritable, afford physiological
examples. The surface soreness and sensitiveness which exist in the
febrile chill, in wounds, dermatitis and neuralgia give pathological
examples. It is further seen in certain cases of meningitis (cerebral
and spinal), spinal irritations, rabies, tetanus and neuritis.
=Hyperæsthesia to cold= is seen in neuralgia, rheumatism, the early
stages of many fevers (chill), in myelitis, neuritis, nerve injuries,
and in posterior (superior) spinal sclerosis.
=Hyperæsthesia of the muscles= may be noted in tetanus, muscular
rheumatism and neuralgia.
_Visceral hyperæsthesia_ is shown in many cases of spasms of involuntary
muscles (colic, arrest of intestinal calculi, gall stones or urinary
concretions), and in inflammation of serous membranes (pleurisy,
peritonitis).
=Paræsthesia.= This is a painful or morbid sensation caused by a lesion
in the central nervous structures or in the nerves, but referred by the
sufferer to some peripheral organ over which such centre presides. It
may even be referred to an organ or part that has been amputated or
otherwise removed. This may cause lameness of a kind to indicate
suffering in a given muscle, tendon or joint, when the cause is purely
central. In dourine, sexual acts are excited which have their real
source in the nerve centres. The rabid dog snaps at imaginary flies in
mid-winter, when such insects are only phantoms of his brain.
=Pressure on a nerve trunk= induces sensations of tingling, vibration,
formication, heat, cold, and paresis, referred by the mind to the part
to which that nerve is distributed, and when the pressure is removed
these sensations recede in the order in which they came. This may
explain some occult cases of lameness.
=Itching= may be a pure, persistent neurosis without any skin lesion.
Treatment should then be addressed to the nervous system.
=Anæsthesia=, or absence of sensation, is in its degree partial or
complete. The latter is familiar as occurring in parts the sensory
nerves of which have been cut across, also in parts the sensory nerve or
nerve centres of which have become completely degenerated. There is no
response to the prick of a needle, the touch of a hot wire, to pinching
or cutting. If the nerve remains intact as far as the spinal centres,
reflex action may still occur, but the patient himself has no
consciousness of this nor of the injury causing it. Accordingly, he
makes no movement of head, ears, eyes, or other parts still dominated by
the brain.
In =partial or imperfect anæsthesia= the response to irritation is less
marked and may be even delayed. In some forms of central lesions the
response to a prick may be delayed two, five, or ten seconds, or even
more.
_Anæsthesia_ causes awkwardness or uncertainty of movement, especially
if the subject is blindfolded.
_Anæsthesia_ may be =induced by medicine=, as in the general anæsthesia
of etherisation, or the local anæsthesia caused by the topical
application of cocaine or carbolic acid.
=Analgesia=, or insensibility to pain, may be present in cases in which
ordinary sensations are still felt. It may be caused by cocaine,
alcohol, and to some extent by carbolic acid.
=Hyperalgesia= is the opposite of this condition, and may be seen in
certain irritable conditions of the nerve centres.