Abstract
A method has been devised by which it is possible to stimulate a nerve-muscle preparation from a frog without contact between the tissue and the electrode.
The essential principle of the method is the placing of the nerve in the vicinity of, but insulated from, an induction coil. The coil is supplied with energy by an oscillator and suitable amplifier. The preparation is arranged in connection with a kymograph in the usual manner.
Two different exciting coils have been employed thus far. Each is wound with insulated copper wire upon a bakelite bobbin and in each the windings are infiltrated with bee's wax. Each is entirely enclosed in a bakelite case. The body of each contains a lumen, running horizontally through its center from end to end, large enough to admit the sciatic nerve of a frog. In the smaller of the coils (coil 1) the lumen is lined with bee's wax. In the larger coil (coil 2), the lumen is large enough to hold a glass tube, into which the nerve is inserted. Coil 1 has about 500 turns of wire and coil 2 about 700. In coil 1 the minimum distance between the nerve and the nearest wire is about 1 mm.; in coil 2 it is about 2 mm. It will be seen that, in coil 1, nerve and wire are separated by bakelite and wax, and, in coil 2 by bakelite and glass. It has been found that good contractions could also be obtained with either coil, without inserting the nerve into the lumen at all, but by threading the nerve through a glass tube and strapping the tube across the bakelite front of the coil with tape.
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