Experimental physiology / by Sir Edward Sharpey-Schafer.

  • Sharpey-Schäfer, E. A. (Edward Albert), Sir, 1850-1935.
Date:
1934
Catalogue details

Licence: In copyright

Credit: Experimental physiology / by Sir Edward Sharpey-Schafer. Source: Wellcome Collection.

    96/184 (page 84)
    THE HEART (continued) Cardiac Nerves of Frog Destroy by a wire the spinal cord of a frog, and also remove the cerebral hemispheres ; this can be done without special dissection by cutting away with a razor the upper jaw and anterior part of the skull at the level of the front of the tympana (see Fig. 88, p. 137). The posterior part of the brain with the medulla oblongata must not be injured. Fix a pair of pin-electrodes connected with an induction coil into this part of the skull and arrange for tetanisation of the medulla oblongata—using the Helmholtz method (p. 17). Lay the frog upon its back on the frog-cork, and fix it securely by strong pins ; expose the heart and the chief nerves which are proceeding from the base of the skull to the hyoid region (vagus, glosso-pharyngeal, and hypo- glossal ; see Fig. 62). The vagus gives off a small branch on each side, which runs close along the superior vena cava to the sinus venosus. Place one vagus trunk upon a fine pair of wire electrodes (which must be fixed by plasticine to the frog-cork, not held in the hand), and connect these electrodes, and also those which are fixed into the skull, to a commutator without cross wires so that the faradising shocks can be sent to one or other pair as may be desired. Place the cork below the lever of the frog-cardiograph, and by means of a thread and fine hook attach the apex of the ventricle to the short arm (Fig. 61). Record the contractions of the heart upon a very slowly moving drum (one revolution in five minutes). Use the “ stop ” for adjusting the lever and for readjusting it after removal from the drum, so that the pressure of the lever point is always exactly the same. Without this precaution the strength of the contractions may be wrongly judged, for if the lever is pressing more at one time than at another, the lever will not be raised so high, even if the force of the heart’s contractions is unaltered. Be careful not to injure the heart. In order to fix it securely, pass a strong pin close to its base and through the vertebral column into the frog-cork. The following experiments may be performed upon this prepara- tion :— 1. Trace an abscissa recording upon it, by an electro-magnetic