. Practical electricity in medicine and surgery. ary cir-cumstances, of retaining a charge ofelectricity. It further shows us thatthe human body partakes somewhatof this property of metals, in that itallows electricity to pass through -see, then, that bodies may bebroadly divided into two groups,—those which retain electricity onthemselves, and those which allow itto flow off. The latter are calledconductors, the former non-conductors or insulators. As inmost classifications, however, so in this case, the distinction be-tween the classes of bodies fades away at certain points. If weshoul
. Practical electricity in medicine and surgery. ary cir-cumstances, of retaining a charge ofelectricity. It further shows us thatthe human body partakes somewhatof this property of metals, in that itallows electricity to pass through -see, then, that bodies may bebroadly divided into two groups,—those which retain electricity onthemselves, and those which allow itto flow off. The latter are calledconductors, the former non-conductors or insulators. As inmost classifications, however, so in this case, the distinction be-tween the classes of bodies fades away at certain points. If weshould arrange all known substances in the order of their con-ducting power we should find, at some place in the list thusformed, a number of substances which might be called indiscrimi-nately either poor conductors or good insulators, just as in chem-istry there are certain elements which strictly belong neither to thegroup of metals nor to the group of non-metals, and, in biology,living things which are neither of animal nor of vegetable origin,. Fig. 1.—Coulombs ToesiokBalance. 8 PRACTICAL ELECTRICITY IN MEDICINE AND SURGERY. but are allied to both groups. For practical purposes, however,the line of separation is broad enough, and the following tablesshow with sufficient accuracy the order of a number of sub-stances arranged according to their conducting or insulatingpower:— CONDUCTORS. 1. All metals. 6. Metallic ores. 2. Charcoal. 7. Sea-water. 3. Plumbago. 8. Rain-water. 4. Dilute acids. 9. Living animals. 5. Saline solutions. 10. Flame, etc. NON-CONDUCTORS. 1. Shellac. 10. Gutta-percha. 2. Amber. 11. Silk. 3. Resins. 12. Marble. 4. Sulphur. 13. Camphor. 5. Wax. 14. Chalk. 6. Glass. 15. Mica. 16. Oils. 8. Diamond. IT. Metallic oxides, etc. 9. Ebonite. Induction.—Let us observe the effect of suspending a glassrod, which has been rubbed with a silk handkerchief, within ahollow metallic vessel (Fig. 2), which completely surrounds it,the vessel itself being suspende
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