as a means of producing the constant current, or that of Voltaic induction, the following are worthy of notice.

4. The large zinc-carbon batteries constructed by Stöhrer, because they consume, when not in use, neither zinc nor acids, though applicable in the same cases as the foregoing, and because they are furnished with a convenient regulator of the strength of the current. They consist of a greater or less number of zinc-carbon elements (without clay cells), which, secured to a beam in the middle of the battery, may be raised and lowered. In the cylindrical pieces of carbon is a deep hole with a diameter of about one-third of an inch, which is filled with sand and closed with a glass stopper, and serves for taking up nitric acid or concentrated chromic acid. Entire, well-amalgamated zinc cylinders encircle the carbon, and are prevented from coming in contact with this by means of glass isolators fastened to it. Glasses, which stand on the pedestal, and into which the elements may be lowered, serve for holding dilute sulphuric acid (16); according as the elements sink more or less deeply into this, the current is more or less strong. When not in use, the carbon and zinc are lifted so high, that the sulphuric acid no longer comes in contact with them, and, as the acid in this case takes up only the lower third of the glass, it may be transported without danger; besides, as there is no consumption of zinc, or decomposition of acid, the apparatus may stand for months without needing a new filling, and being always ready for use. Moreover, the elements may be united, as in the two following batteries, by means of clamps of copper plate, into one or several pairs.'

The most convenient apparatus for the application of the constant current to medical purposes is

1

1 [In an article on Organic Infantile Paralysis contained in the QUARTERLY JOURNAL OF PSYCHOLOGICAL MEDICINE AND MEDICAL JURISPRUDENCE for July, 1868, I have described Stöhrer's original battery at length. The accompanying woodcut (Fig. 4) will serve better than any additional description to give

5. Remak's zinc-carbon battery. This generally consists of sixty elements, which have the following proportions:

an idea of its form. Stöhrer has recently greatly improved this battery by reducing its size, and altering the arrangement for getting the current from any number of cells.-See Appendix. W. A. H.]

In a glass, 15 cm. high, and 11 cm. in diameter, there is a coil of one-inch-broad copper plate, to which there is soldered a copper wire which passes vertically upward through a glass cylinder, 2.5 cm. wide, and serves to connect with the next standing element. This glass cylinder, cemented into the bottom of a clay cell which covers the copper plate, is filled with water and pieces of blue vitriol up to its edge. At the upper part of the clay cell, surrounding it, and reaching to the bottom of the glass, there is a compressed layer of papier-mâché to the height of from 6 to 7 cm., on which, separated by a layer of fustian, rests a zinc cylinder, 1 cm. thick and three times as high. This modification of Daniell's elements by Siemens and Halske has the advantage, through limiting the chemical process within the battery, of lengthening the durableness of the apparatus in this way, that the same may be used many months without repairs, if we only take care, every three or four weeks, to fill the glass cylinder with crystals of blue vitriol. It is advisable to clean the battery every three or four months, by which means the zinc. is made more active; the security of the copper wire may then be tested, injuries may be repaired, and more acid water may be added, till the zinc is covered. These sixty elements, placed one behind another, are brought in connection with the current selector, rheotrope, and the galvanoscope, which three instruments are secured to a polished mahogany board.

The current selector, which has for its object the uniting for effect any number of elements, even as high as sixty, has the following construction: It has ten silver-plated buttons, arranged in opposite half-circles of fives, bearing the numbers 10, 8, 6, 4, 2, 10, 20, 30, 40, 50, which indicate the number of elements with which they are in combination. In the middle of each half-circle is a winch, which, moved from button to button, shuts off any desired number of elements. If we, for instance, need forty-two elements, we turn the winch B2 to 40, the winch B1 to 2; while, if we wish to use six

elements, the winch B2 is moved to the nail O lying between the two half-circles, the winch B1 to 6. When both winches are at O, there is no current flowing.

The change of the direction of the current is effected by means of the commutator C, in connection with the points

N (normal) and W (reversed). The conducting wires being secured by the binding-screws K (copper) and Z (zinc), the positive current passes, when the winch of the commutator is on N, through the clamp K and the conducting wire into the body, and through the other conducting wire to the zinc pole Z. If, on the contrary, the winch is on W, the positive current passes from the clamp Z through the body to K.

The galvanoscope G shows us, when the tips of the conducting wires are placed on any part of the body, and the stopper a is removed, how strong the current is, by means of the amount of deviation from the O point. On the brass button above the galvanoscope there is a small magnet-rod, by turning which to the left or the right we can place the needle on the point, when this shows a deviation, the circuit being open.

The combination between the battery and the current selector is made in the following way: After the individual elements are arranged behind one another, and the zinc always connected with the copper, the first conducting wire of the copper pole of the first element is carried to the button 10 of the winch B1, and there secured by means of a screw. The second wire is fastened into the clamp which unites the second element with the third, and carried to the button 8. The same takes place between the elements 4 and 5, 6 and 7, 8 and 9, and the wires are united with the buttons 6, 4, 2, in a corresponding order. The wire between the tenth and eleventh elements is connected with the button 0. From the eleventh element on, the enumeration is always by ten elements; the conducting wires are set on between the twentieth and twenty-first, the thirtieth and thirty-first, the fortieth and forty-first, and finally the fiftieth and fifty-first, and carried thence to the buttons 10, 20, 30, 40, of the winch B2. The last wire is carried from the zinc pole of the sixtieth element to button 50.

Remak's electrodes consist of wooden handles with brass