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knife is suddenly lessened, and the latter immediatelyrecovers its lost quantity of fluid from that bodywhich, by vicinity and conducting character, is mostsuitably disposed to supply it. In the present case,this supply is from the limbs of the frog, nearestto the knife, which, though long detached from therest of the animal, retains sufficient irritability, orsensitiveness, to become convulsed by each of thesemomentary discharges.

By directing your attention to figs. 6 and 26,pages 36 and 81 (lectures on Electricity), you willeasily understand that in this experiment, the limbsof the frog became as decidedly electro-polar as theblade of the knife. And in order to convince youof this fact, I will now introduce a perfectly novelexperiment amongst our illustrations.

I have here arranged the hind limbs of threefrogs in nearly the same right line with the axis ofthe prime conductor of the machine. They areFig. 2.

insulated from one another, and also from the table,by resting on small slips, or tables, of varnishedglass, which are supported on glass stems. I alsohang from each pair of limbs, two pair of pith balls,as represented by fig. 2. When the machine is putinto action, a divergency takes place in every pair ofthe electrosopic balls, which, by testing in the usualway, are found to be negative and positive alternately,in precisely the same manner as if suspended fromthe extremity of a series of metallic wires when ex-posed to a similar electric influence (see Electricity,fig. 6, page 36) ; and, consequently, each pair oflimbs is polar, being negative in those extremitieswhich are directed towards the prime conductor, andpositive at the remote extremities.