The Dangers of Electrical Currents

Abstract

ON account of the widespread use of electricity at the present time, the small book before us, by M. Rodet,1 is of considerable practical value. We note that an actual current must pass through the tissues of the body if any effect is to be produced. A static charge is harmless. A bird may perch on a high-tension main without any serious results. The resistance of the human body resides chiefly in the skin, and is very high if the skin is dry-from 20,000 to 80,000 ohms. But if the skin is moist and a good earth contact is made by bare feet in a wet mass, a man may be killed by touching a ico-volt main. A brief summary is given of the general physiological effects of stimulating various nerves by electrical currents. The development of heat is also discussed: burns are produced where the current density is great, as when it enters by a relatively small contact surface. With respect to high-frequency alternating currents, the interesting experiments of Kennelly and Anderson in America are described. They showed that, at an alternation of 100,000 per second, a voltage of 250 can send a current of half an ampere through the body without any sensation beyond that of warmth. The explanation is probably that given by Nernst, namely, that certain ions in the nerves must attain a certain minimal local concentration in order that stimulation may take place. Each half-wave of so rapid an alternation cannot, in the time permitted, effect this concentration before the opposite half-wave comes in and reverses what little has been done. The energy of the current is thus converted into heat without being able to produce electrolytic changes.