. Advanced lessons in practical physiology for students of medicine. Physiology. LESSON II MUSCLE AND NERVE (Continued) MYOGRAPHY 1. The Construction and Action of the Dry Cell.—The electric method of stimulation is employed most frequently in the laboratory because it is the most convenient. The electric enereiy is derived, as a rule, from a Voltaic cell. As a generator may be employed a Daniell, Grove, or Leclanch6 cell. The moist cells, however, have been dis- placed in the course of time by the so-called dry cells which give off no fumes and acids, need no refilling, and give, as a rule, g
. Advanced lessons in practical physiology for students of medicine. Physiology. LESSON II MUSCLE AND NERVE (Continued) MYOGRAPHY 1. The Construction and Action of the Dry Cell.—The electric method of stimulation is employed most frequently in the laboratory because it is the most convenient. The electric enereiy is derived, as a rule, from a Voltaic cell. As a generator may be employed a Daniell, Grove, or Leclanch6 cell. The moist cells, however, have been dis- placed in the course of time by the so-called dry cells which give off no fumes and acids, need no refilling, and give, as a rule, good service at slighter cost. The dry cell connnonly used is a modification of the Leclanche cell. It consists of a jacket of zinc lined with plaster of Paris and saturated with ammonium chlorid. Its inner space is taken up by a carbon plate which is surrounded by black oxid of manganese. The plate of carbon projecting from this mixture forms the posi- tive pole or anode, whereas the negative pole or cathode is represented by the zinc. Electricity "flows" from a place of high potential to a place of low potential. Hence, if the carbon and zinc of the battery are con- nected by means of a conductor, say, a copper wire, a current is set up which leaves the generator at the former pole and enters it at the latter. Inside the cell the current flows from the zinc to the carbon to complete the circuit (Fig. 2). The difference in the potential between the two poles of a battery constitutes the electromotive force. It is maintained by the interaction of the chemical substances con- tained in the battery. The latter, therefore, corresponds to a reservoir of electricity which remains filled as long as there is enough material present to yield chemical energy. When this material has been used up, the difference in the electric po- tential disappears and the current ceases. In its passage through wires the electric current loses a certain amount of its initial energy, owing to
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