Text-book of physiology : general, special and practical / by John Hughes Bennett.

  • Bennett, John Hughes, 1812-1875.
Date:
1872
Catalogue details

Licence: Public Domain Mark

Credit: Text-book of physiology : general, special and practical / by John Hughes Bennett. Source: Wellcome Collection.

Provider: This material has been provided by University of Bristol Library. The original may be consulted at University of Bristol Library.

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    trolled by a spring, d, which may be tightened or relaxed, e. Fixed weight acting as a counter-poise to c. /. End of the'rectangular arm seen at n', Fig. 1, and h, Fig. 3. The arrow to the right shews the direction in which the box revolves. Fig. 3. Diagram shewing the arrangement of apparatus for determining the rapidity of the nerve-current, a. Forceps holding femur; b. gastrocnemius muscle; c. sciatic nerve; d. revolving cylinder; c. lever carrying the stylette;/. centrifugal apparatus; g. steel spring forming the bridge between the two pillars Ic i; h. end of out-springer, and above it the end of the rectangular arm; t wire passing from primary coil m to one side or pier of the bridge in the myographion; i. wire from tlie other pier back to the battery I; I. the battery ; m. primary coil of induction machine; n. secondary coil; n n. Pohl's Commutator, having at p3, i wires going to stimulate a portion of the nerve c, close to the muscle at r, and at o 1, 2, wires passing to q, so as to stimulate at a distance from the muscle. The primary circuit is in the direction I, m, k, g, i, back to I. When this is broken at g, an induced current is sent from n either to r or q, on the nerve c, according as we place the Commutator. Fig. 4. Du Bois-Reymond's key. B. Vulcanite plate, b, c. Rectangular pieces of brass, each bearing two screws. These may be connected by means of the handle d. Fig. S. Pfliiger's Myographion. S. VVooden stand. B. Frame having a groove in which the glass plate P moves. F. Brass pillar bearing a square glass chamber for the muscle. L. For- ceps for the femur, to which is attached the gastrocnemius muscle A with the sciatic nerve N. a. Brass pillars bearing at the top the double lever b ; c. swivel apparatus for connecting the lever b with d, a long hook attached above to the tendo AchiUis; g. a scale for a weight sufB- cient to draw down the lever after it has been elevated by the contraction of the muscle ; m. movable weight for carefully balancing the lever. Fig. 6. Pohl's Commutator, a. A round wooden disc, having six small holes fdled with mercury, each having a screw for the attachment of a wire ; -f a. wire coming from positive pole of battery; —b. wire going to negative pole ; P O. two pieces of wire permanently fixed at one end into -|- a, and — b, and the other ends held in close proximity by a glass tube S ; q, r, and m, n. transverse arcs of wires, having their ends free, so that by moving the bridge P S 0, the ends of the arcs may dip into either the holes a /3, as seen in tlie figure, or into A B ; a /5. attachments for wires going to a nerve or muscle; A B. another pair of the same ; h and i, transverse wires, h being bent in the middle so as not to touch i. The direc- tions of the current may be as follow : (1.) WilJiout the transverse wires, h i. In this case, the current will pass along a circuit, « /3, when the ends of the arcs dip into the holes r n ; but if the bridge be reversed, so that the ends q, r of the arcs dip into A B, the cur- rent will pass along a circuit from A to B. (2.) With the transverse wires h i. We can now send a current from « to i3, or from pi to «, that is, either up or down a nerve. As the bridge is placed in the figure, the direction will be + a, P, r, a, /3, n, 0,—b, and from thence to the battery. But if we now reverse the bridge, so that q m dip into the holes A B, the current will travel along the cross wires thus, -|- «, P, q, A, cross wire h, n, (i, a, r, cross bar i, TO, 0,—h, and from thence back to the battery. Fig. 7. Form of tracings to be obtained on the cylinder of the Myographion. The hori- zontal line a 6 is the mark made by the stylette during the revolution immediately before the primary current is broken. The two oblique curved lines c e,d fare produced by the stylette being drawn upwards by the contraction of the muscle when the nerve is stimulated. Of these two, the line c e is that produced when the stimulus is applied close to the muscle ; while (J/is caused by the contraction when it is applied at a distance from the muscle. The short distance between the points where these curves leave the horizontal line c d indicates the length of time the nerve current occupied in passing from the distant to the near point of stimulation.