On an electrical bench for physiological research / by R. Milne Murray.
- Murray, Robert Milne.
- Date:
- [1891]
Licence: Public Domain Mark
Credit: On an electrical bench for physiological research / by R. Milne Murray. Source: Wellcome Collection.
Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.
5/14 page 3
![circuit of Ng, and galvanic stimuli will be transmitted to the nerve by the electrodes X leading from the commutator V, and the direction of these stimuli can be altered by this commutator. The effects of the currents transmitted by the relay K through the coil can be adjusted approximately by shifting the coil R in relation to P, and those from I can be adjusted by increasing the strength of the battery Ng, or by inserting resistances in the circuit. But a more accurate method of adjusting the strength of those currents will be described later. It is sometimes necessary to cut out the induced current in R at the making of the current in P, or the induced current in R at the breaking of this current. This is effected by the relay L, which is a sort of “ rocking shunt.” The mercury cups Ml and Mg in the relay L are joined by wires to the terminals of the secondary coil R. These are shown by the lines mm. Now let the platinum contact M^ dip deeply into the mercury while that at Mg is just clear of it. Let the plugs H3 and be withdrawn. It will now be seen that the relay L will act at the same moment as the relay K, and the induced current in the secondary, produced at the making of the current in the primary, will find an easy path between the mercury cups M^ and Mg, because the platinum-point Mg will be dipped in at the moment the relay K sends the current through the primary P. But the breaking current will have to pass through the nerve, because the relay L will give at the same time as K, and the point Mg will be withdrawn from the cup, opening the shunt between M^ and ]\Ig. By reversing the adjustment of M^ and Mg, the “ break- ing ” current may be cut out and the making ” transmitted. The mode of adjusting the strength of the currents indi- cated above is sufficiently accurate for demonstration, but is deficient in accuracy for refined research. For this pur- pose in the bench under consideration, advantage is taken of the principle of the Wheatstone’s Bridge. For adjusting the strength of the Faradic stimulation, the arrangement is as follows :— The coils P and 8 (the ]wimary and secondary), Plate](https://iiif.wellcomecollection.org/image/b24930131_0005.jp2/full/800%2C/0/default.jpg)
