Electro-medical instruments and their management : and illustrated price list of electro-medical apparatus / by Schall & Son.

  • Schall & Son.
Date:
1911
Catalogue details

Licence: In copyright

Credit: Electro-medical instruments and their management : and illustrated price list of electro-medical apparatus / by Schall & Son. Source: Wellcome Collection.

    19/252 (page 7)
    APPARATUS FOR GALVANISATION AND ELECTROLYSIS. The Resistance of the Human Body varies widely. If two small metal electrodes of one centimetre diameter each are placed on the dry skin, the resistance will be near 100,000 ohms. If we use, however, larger electrodes, about 5 centimetres diameter, cover them with leather, and place them on the skin, after having well soaked them in warm salt water, the resistance will not be more than about 3,000 ohms, and become less, within a short time, under the influence of the current itself. If we introduce an electrode into the rectum, and place a large electrode, 8 inches diameter, on the abdomen, the resistance will be less than 200 ohms. It is principally the skin which offers the great resistance, whereas the blood, etc., conduct comparatively well. Still, we have in most cases 1,000 to 5,000 ohms resistance to deal with, and therefore a large number of cells is indispensable in order to obtain with these resistances currents varying between 1 and 50 or even more milliamperes. Which are the most suitable Cells ?—It is not my intention to enumerate all the cells which have been invented since Volta till to-day. Any cell can be used which is capable of yielding the desired strength of current; but if we consider convenience, portability, etc., the number of useful cells is limited. In choosing a battery, it is a consideration whether it can be charged by the owner himself, or whether it has to be returned to the maker when exhausted. The cells most frequently used may be classified in two groups : Cells which contain acids, and where the zincs therefore have to be taken out of the fluid after the battery has been used—Plunge Batteries ; and cells, the exciting fluid of which does not attack the zinc as long as the circuit remains open, and in which the zinc may remain immersed. Leclanche Cells.—Let us first consider the cell which is more used than all the other cells taken together—the Leclanche cell. For galvanisation and electrolysis, there can hardly be found a cell more reliable and convenient than the Leclanche cell. It is always ready for use, and a well-constructed cell will last for two years without having to be seen to during that time. Moreover, they can be cleaned and refilled without technical aid. Dry Leclanche Cells.—If portability has to be considered, the dry cells, which belong to the Leclanche type, too, have great advantages over the cells containing fluid, for there is no liquid to be spilled or to corrode the brass parts, and there is no glass, etc., to get broken. They can be sent charged all over the world, and are very suitable for batteries which have to be carried about frequently. Their only disadvantage is that the cells, after being exhausted, cannot be recharged, but have to be replaced by new ones, and this makes the refilling rather expensive. On the other hand, batteries filled with good dry cells will certainly last for fully two years without requiring recharging, and they are less likely to require repairs than those filled with liquid, because accidents . w z . o z h2 < E- CO < 5 2 OS * < > o < o 6 w O c ft X X 3 2 co H . o >• s oc . W to H Qu => £ < < O <u gj hoc . X ©H •*- H cO X Q O < ** 0 . CQ C S| 1 E