A laboratory manual of electrotherapeutics . for the electric cautery. The strength of current required for heating electriccauteries varies from i to 25 amperes. This current isfar in excess of that used in therapeutics when the currenttraverses the body, and for this reason special forms ofgenerators and controllers are required for doing cauterywork. A suitable current may be obtained from:— 1. Primary batteries. 2. Secondary or storage batteries. 3. The dynamo. Primary Batteries.—Since the external resistancein a cautery circuit is very small (seldom exceeding . 1ohm) it is necessary that
A laboratory manual of electrotherapeutics . for the electric cautery. The strength of current required for heating electriccauteries varies from i to 25 amperes. This current isfar in excess of that used in therapeutics when the currenttraverses the body, and for this reason special forms ofgenerators and controllers are required for doing cauterywork. A suitable current may be obtained from:— 1. Primary batteries. 2. Secondary or storage batteries. 3. The dynamo. Primary Batteries.—Since the external resistancein a cautery circuit is very small (seldom exceeding . 1ohm) it is necessary that a cautery battery should be 6o LABORATORY MANUAL specially constructed so that its internal resistance shallbe reduced to a minimum. The E. M. F. may vary from2 to 6 volts. In order to deminish the internal resistanceof a battery, the plates should be large and near together,and every precaution should be taken to prevent polariza-tion. If cells of large size are inconvenient and makethe battery too cumbersome, smaller cells may be em-. Fig. 32. ployed provided they are joined in multiple arc. Byusing a large bichromate cell with large plates of carbonand zinc the resistance may be brought down to .15 cell acting through a cautery electrode of .1 ohmresistance would furnish 8 amperes of current. E amperes. C R C = In all forms of primary batteries which generate largecurrents, polarization soon tends to lessen the output ofcurrent. This difficulty may be prevented by keeping the OF ELECTROTHERAPEUTICS. 61 plates of the battery constantly in motion, thus bringingfresh battery fluid in contact with the plates. By havingat the outstart a current capacity far in excess of theamount required to heat the cautery, a suitable rheostatin circuit to regulate the current to the required amountwould be the most convenient method of overcoming thepolarization effects. Secondary or Storage Batteries.—A well con-structed and newly charged storage battery furnishes a
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