(c) The sensibility of the skin to caloric is usually the last to disappear in the progress of an organic lesion, so that in certain cases (injury to nerves or spinal cord, myelitis, etc.) testing by ice or by a burning object is a sort of last resort. Before deciding in a given case that there is a complete break in the sensory tract, this test should be used as well as the application of the most intense induced electric current delivered upon the dry skin by a wire end.
In some cases of partial anæsthesia (e.g. in posterior spinal sclerosis) cold may be felt as heat and vice versâ, or pinching may be felt as burning, and be quite persistent.
(d) The so-called muscular sense may be greatly impaired or lost without ordinary anæsthesia. In such a case the subject is no longer directly and spontaneously aware of the exact position of his limbs, of passive motions done to them, and he executes voluntary movements with uncertainty. He is also unable to judge correctly of differences of weight in objects successively placed in his hand or hung from his foot. He needs the aid of sight to guide the affected limb and to judge of its position, etc. The awkwardness and uncertainty in voluntary movements by impairment of muscular sense must not be confounded, as is sometimes done, with ataxia, in which the attempted volitional movement is jerky and oscillatory, owing to the inharmonious action of antagonistic muscular groups.
(e) When a strong induced electrical current is passed through a muscle by means of wet electrodes applied to the skin, so as to cause a strong contraction, a special quasi-painful feeling, akin to that of cramp, is experienced in the contracting muscle, and is clearly distinguishable from the cutaneous sensation. This, the electro-muscular sensibility, may be lost independently of other modes of feeling and without loss of contractile power.
(f) Some observers claim that a special mode of sensibility exists in the skin by which varying degrees of pressure are estimated, independently of traction upon tendons and muscles (muscular sense), and that this may be separately impaired or lost.
(g) Visceral anæsthesia shows itself in the ordinary way by loss of that feeble degree of common sensibility which the internal organs possess, and also by impairment of their special functions, giving rise to anorexia, hydroadipsia, retention of feces and urine, loss of sexual feeling (without progenital anæsthesia). Of course, these symptoms may be due to other conditions, and each case must be carefully studied. In the insane, visceral anæsthesia gives rise to delusions of emptiness, destruction of organs, and even, if coinciding with general cutaneous anæsthesia, to the notion that the body is dead or absent.
A singular phenomenon often witnessed is retardation in the transmission of an impression (usually a painful one). Thus, in testing the sensibility of the skin of the legs in tabetic patients, it is observed that instead of the normal, almost instantaneous, appreciation of the impression made by a needle-point, there is a lapse of two, five, ten, or even sixty seconds between the pricking and the signal of sensation by the patient. It should always be determined in such cases whether the retardation is peripheral and actual, or central and due to psychic conditions (dementia, absorption in a delusional state). Thus, in a case of profound melancholia we may observe extreme slowness and dulness of sensory impressions or complete anæsthesia; but the symptoms would have a very different significance, diagnostic and prognostic, from the same noted in a mentally clear patient.
An important result of impairment of sensibility is a reduction or loss of reflex movements originating from the area or organ which is anæsthetic. This is shown in anæsthesia of the distribution of the trigeminus when the reflex protecting movements of the eyelids no longer take place, in atrophy of the optic nerve when the pupillary reflex actions are lost. In posterior spinal sclerosis we see several illustrations of this law: progressive degeneration of nerve-fibres in the posterior root-zones of the spinal cord, causing loss of patellar reflex, of vesical, rectal, and sexual reflexes, and in most cases of cilio-spinal reflexes and of muscular tonus. In these and analogous conditions one arc of the reflex mechanism is deranged, centripetal conduction is interfered with, and the reflex motor discharge can no longer be evoked.
That a similar pathological condition occurs in the cerebral mechanism, and may serve to explain many psychic symptoms, is very probable.