Medical Jurisprudence, Forensic medicine and Toxicology. Vol. 1

by R. A. Witthaus; Tracy C. Becker

The resistance of 236 men employed at Messrs. Bergmann & Co.’s Electrical Works in New York appears to have averaged 1,184 ohms and to have varied from 1,870 to 610 ohms. These measurements were also taken between the hands, which were washed with soap and water and then dipped in jars containing a solution of caustic potash. The battery consisted of four chromic-acid cells each having an E. M. F. of 2 volts.

As shown in all the experiments on animals and more especially in the cases of electrocution, the continuance or duration of the current has much effect on the resistance. As the current continues the resistance diminishes. Thus in the case of McElvaine the resistance between the immersed hands was at the beginning 800 ohms and at the end of the contact of fifty seconds had decreased to 516 ohms. In this case, when the current of 1,500 volts was applied from the forehead to the leg, the resistance was practically steady at only 214 ohms. Of course the small resistance in these cases (electrocutions) depends largely on the perfect contact secured.

According to the amount of resistance offered do the effects of severe shocks of electricity differ. This is shown especially well in the action of lightning, but is also true of powerful currents produced mechanically. If the resistance of the skin be slight at the moment of entering the circuit of a strong current, the current will pass through it with comparative ease and without causing much injury; but if on the other hand the resistance is great, the current will be, as it were, momentarily retarded or stored, heat will be developed, and there will ensue a burning and charring of the tissue of a special kind. These burns occur principally at the places where the current is specially resisted, that is, at the point of entrance of the current to the body and at its point of exit. This is the cause of the frequent burns in the heel or sole of the foot in the case of those struck by lightning while standing, as the electricity passes away from the body into the ground and finds a strong resistance at the point of leaving the body. This is also the cause of the burns where the current leaves the body from any other cause, as from the contact or proximity of a metallic object. The greater the resistance so long as the current passes, other things being equal, the more severe is the burn. It is for this reason that in medical electricity we usually use wet sponges on the skin or electrodes moistened with salt and water or with other fluids which will assist in rendering the passage of the electricity through the skin more easy. Solutions of chlorid of sodium and of certain other salts do this.

The mechanical effects of currents vary thus according to the resistance encountered. They also vary according to the intensity or concentration of the current. If a current of moderate force be applied through a small metallic point, it will burn, pain, and produce active irritative symptoms, while if the same amount be applied over a large surface simultaneously, it may have little or no irritating effect. We have, therefore, three factors in determining the mechanical effect of any electric current on the body: (1) the condition of the body, that is, the amount of resistance which the current will encounter at its entrance and exit; (2) the amount and intensity of the current; and (3) the character of the current. For practical purposes of the more severe currents we have only to deal with the continuous and alternating.

SYMPTOMS.

Direct Symptoms.

The direct symptoms produced by powerful mechanical currents of electricity may be divided into three classes: I. The mechanical; II. The essential or internal; III. The mental or psychical.

These classes are fairly distinct, but they are not absolute, and certain symptoms are on the borders.

The most important mechanical symptoms produced by these currents are burns. These occur at all points of strong resistance externally, hence especially at the points of entrance and departure of the current. They vary from all grades, from the lightest possible, where only the fine hairs on the skin are singed, to those of extraordinary depth and severity. The characteristic burn from powerful currents is, however, well distinguished. It consists in a deep hole of various shapes with clear-cut edges surrounded by an inflamed area and containing in its cavity a mass of blackened tissue which only separates from the portions below after several days, and causes a wound which, though not very painful, heals very slowly. The severity of electric burns is often at first sight underrated, and their duration, when severe, is unexpectedly long. It occasionally happens that after a burn of this character appears nearly healed, the surrounding and, in appearance, healthy tissue breaks down, perhaps under a healthy skin, and a destructive process occurs which much retards recovery. This is evidently due to tissue destruction from a strong electric current of such a character as to produce necrobiosis without the external appearances of a burn. These burns are, perhaps, oftenest seen on the hands, but this is only because these parts are more likely to come into contact with the current. They may occur in any portion of the body.