Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.

the end of which time, as before, there could be produced no contractions ; but this power was regained afresh, as before, upon the simple reversing the direction of the current, and then open- ing and closing the circuit. By such means he produced changes from half hour to half hour, and even more frequently, and was able, for an entire day or longer, first to annihilate and then to restore at pleasure the natural excitability of the nerves and muscles of a mutilated animal. This is the origin of the term " voltaic alternatives.'''' The results of the alternate use of galvanic currents we shall learn to be of the greatest importance in the details of electro-medical practice. The new condition worked up by the current in a given direction, and still more manifested by given careful and definite variations, we may understand to be a condition which, from analogy with what takes place in all other cases, must be a polarization of the molecules of the nerves, alternating with the molecular dis- charges. So long, he says, as the nerve has sufficient vitality, and hence irritability, left, it reacts just as soon as the current ceases; i. e., it resumes its natural molecular state; but if the animal is mutilated, killed, or abused by the experiments of repeated currents, there is soon obtained a toning- down, or rather, probably, an exhausting of the nerve resources, which is shown, by this reaction no longer taking place; therefore a current of electricity given in the opposite direction is neces- sary to restore that state. I will only add here the funda- mental and instructive law laid down by M. Dubois-Reymond : " The motor nerves are not excited so much by the absolute degree of the density of the current of electricity, as by the variations that occur in the sum of this density, — from one instant to another ; the excitement from these changes being greater in proportion as they take place more rapidly, or as they are more considerable in a given time." Electricity, therefore, acts upon the animal body, both in health and disease, in a manner that all scientific observers acknowledge to be peculiar to itself, and producing results other- wise unattainable. Dr. Galvani, as we know, was the first to produce muscular contractions by the aid of galvanic electricity.