[Illustration: FIG. 4. Contraction of Paralyzed Muscle on thirty-first day of Bell's palsy of the face. CaCC. 20 El. (Amidon). Shows retarded contraction and slow contraction, with tendency to tetanus.] [Footnote 2: “The Myography of Nerve-degeneration in Animals and Man,” _Archives of Medicine_, viii., No. 1, 1882.] In the period of recovery or regeneration of the nerve the musculo-galvanic reactions slowly reacquire their normal characters; the normal suddenness and completeness of the contractions gradually appear, and faradic excitation causes slight responses. Lastly, the nerve also begins to exhibit excitability under galvanism and faradism. These various abnormal electrical reactions, also frequently observed in diseases of the spinal cord, constitute the so-called reaction of degeneration, or De R. The subject is one of much practical importance, and for details the reader is referred to the treatises on electro-therapeutics of Erb and De Watteville. Just as we depend upon the De R. to prove interruption of motor nerve-fibres (or, in other cases, destruction of ganglion cells in the anterior horns of the cord), so do we rely upon the demonstration of complete anæsthesia to prove interruption of sensory fibres. In seeking for the area of anæsthesia several points must be borne in mind: (1) The normal {68} distribution of the principal nerve-trunks as taught by ordinary anatomical works; (2) the remarkable anomalies of distribution which sometimes occur; (3) that many nerves near their endings exchange filaments in very variable numbers; loops for collateral innervation, which will supply some sensibility to parts which, judging by ordinary anatomical rules, should be made anæsthetic by section of a given nerve-trunk; (4) another consideration is the degree of anæsthesia. Before pronouncing upon the complete and fatal division of a nerve-trunk (by injury or by disease), absolute anæsthesia should be demonstrated in its area of principal and isolated distribution. Ordinary tests are not, as a rule, sufficient for this purpose. The best means in our experience consists in the use of a very strong induction (faradic) current, as follows: The skin of the suspected region to be thoroughly dried and rubbed with chalk or powdered starch; one pole, consisting of an ordinary wet electrode, to be applied just above the part to be tested, and the other pole, consisting of a single wire, with which different parts of the anæsthetic area are to be touched. By this means partially insensible regions, not responding to pricking and burning, may be made to yield reaction, and the area of absolute anæsthesia be thereby much reduced. Malingering may also be readily exposed by this test, which presents another advantage—viz. of not causing local injury or scars as burning will.