Clinical electrocardiography / by Sir Thomas Lewis.

  • Lewis, Thomas, Sir, 1881-1945.
Date:
1924
Catalogue details

Licence: In copyright

Credit: Clinical electrocardiography / by Sir Thomas Lewis. Source: Wellcome Collection.

    15/142 (page 5)
    makes the manipulation of the board relatively slow. But I retain it as an illustration because its circuits and their use are easy to understand and because more complex boards are arranged on similar principles. Fig. 3 is a diagram of the apparatus and its connections. The string of the galvanometer (GS) is connected to a key (K1) which closes the string circuit. The closure of this key brings the string to rest and safeguards it from damage. The same key communicates with two circuits, the inner and outer circles of the diagram ; the former is a shunt* containing a resistance and key (R1 and K2), so arranged that when closed it carries the greater part of the tested current, thus preserving the string from mishap. It is used when a current of unknown strength is thrown into the string circuit. The outer circle represents the main circuit ; it is broken at three points ; (1) at K1 where it joins the string circuit, (2) at C1, by a commutator, where it connects to the patient, and (3) at G2, by a commutator, where it connects to the compensator. It contains also a dial resistance (R5) and the standardises The separate parts of the apparatus may be described briefly and in rotation. Connection of patient. One wire which runs from the commutator C1 to the key K5 may be connected at will to the right arm (R. A.) or left arm (L. A.) by means of the special key ; the second or parallel wire may be connected to the left arm or left leg (L.L.) by the same key.* The actual contacts are made when the limbs are immersed in salt water,f and through porous pots containing zinc sulphate (Fig. 3 B and Fig. 4). The key (Kr°) is arranged so that the two main wires may have the following paired connections. * The wires which connect to the limbs may be of any length ; the patient who is observed may be in a separate building. t The water should be warm and pieces of cotton wool may be added to form a bath of porridgedike consistency. By these means disturbing move¬ ments of hands and water are diminished.