Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.
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iological effects of electric currents on the sentient nerves, we gather the conclusion, that the sensations caused by the applica- tion of the continuous current of electricity are strongest on closing the inverse current, and on opening the direct current; but the contrary takes place when the motor nerves are acted upon; for muscular contractions are more readily produced on closing the direct, ahd on opening the inverse, current; for this reason, therefore, if mixed nerves are electrized, we obtain the following Effects on the Mixed Nerves. — _. , ( Closing the circuit— Contraction. Direct current. \ „ . ., . ., „ ( Opening the circuit—sensation. T ( Closing the circuit — Sensation, inverse current. \ „ . „ . .x ~ ( Opening the circuit — Contraction. When we electrize mixed nerves, the phenomenon that re- sults is due to the peculiar excitation of the filaments of both sentient and motor nerves of which they are mutually composed, and hence, to a greater or less degree, to reflex action. But the direction of the current mainly determines the physiologic and the therapeutic result. Hence, this rule is held to be the funda- mental, viz.: that the direct current can produce powerful mus- cular contractions with comparatively little sensation, or pain; while the inverse current can produce greater sensation, or pain, and that with greater "reflex action;" ivhile the muscular con- traction is comparatively weak, or even totally wanting; also, that the reversing the direction of a current from second to sec- ond, increases its exciting, reflex, and constitutional effects. According W the law first laid dowa by Dubois-Reymond, it is moreover perfectly easy to understand the action of electro- magnetism, and other induction currents upon the motor nerves and muscles. The physiological action is in this case the great- est possible for the given amount of electricity, as to quantity or intensity, that actually courses through the nerves. These currents are necessarily made up of the least conceivable bits of currents, which are instantaneous, succeeding each other with the greatest rapidity, in consequence of the make and break in the inducing current of the battery, or of the approach and leaving of the magnet, &c. But, I ask, must it necessarily fol- 21