“Calcine some common oyster-shells, by keeping them in a good coal fire, for half an hour; let the purest part of the calx be pulverised and sifted. Mix with three parts of this powder, one part of flowers of sulphur. Let this mixture be rammed into a crucible of about an inch and a half in depth, till it be almost full; and let it be placed in the middle of the fire, where it must be kept red hot for an hour at least, and then set it by to cool: when cold turn it out of the crucible; and cutting or breaking it to pieces, scrape off, upon trial, the brightest parts; which, if good phosphorus, will be a white powder.”
EPITOME
OF
GALVANISM.
CHAP. I.
A Short account of the discovery of Galvanism.
This part of our subject has been called animal electricity, by the greater part of those persons who have written upon it;—but this name seems to be improper; for, as an author of reputation on the subject, remarks, “it has by no means been proved that these phenomena depend either upon electricity or animal life.” While this is the case, it is certainly best to distinguish this science by the name of its inventor Louis Galvani. He was an Italian, and professor of anatomy at Bologna, when he made the discovery of Galvanism, which was entirely accidental, as will appear in the following account.
Whilst Galvani was one day employed in dissecting a frog, in a room where some of his friends were amusing themselves with electrical experiments, one of them happened to draw a spark from the conductor, at the same time that the professor touched one of the nerves of the animal. The consequence was, that the animal’s whole body was instantly shaken by a violent convulsion. Astonished at the phenomenon, and at first imagining that it might be owing to his having wounded the nerve, the professor pricked it with the point of his knife, to assure himself whether or not this was the case; but no motion of the frog’s body was produced. He now touched the nerve with the instrument as at first, and directed a spark to be taken at the same time from the machine, on which the contractions were renewed. Upon a third trial the animal remained motionless; but observing that he held his knife by the handle, which was made of ivory, he changed it for a metallic one, and immediately the movements took place, which never was the case when he used an electric, or non-conducting substance.
After having made a great many similar experiments with the electrical machine, he resolved to prosecute the subject with atmospheric electricity. With this view he raised a conductor on the roof of his house, from which he brought an iron wire into his room.—To this he attached metal conductors, connected with the nerves of the animals, destined to be the subjects of his experiments: and to their legs he fastened wires which reached the floor. These experiments were not confined to frogs alone. Different animals, both of cold and warm blood, were subjected to them; and in all of them considerable movements were excited whenever it lightened. These movements preceded thunder, and corresponded with its intensity and repetition; and even when no lightning appeared, the movements took place when any strong cloud passed over the apparatus.—That all these appearances were produced by the electric fluid was obvious.
Having soon after this suspended some frogs, from the iron palisades which surrounded his garden, by means of metallic hooks fixed in the spines of their backs, he observed that their muscles contracted frequently and involuntarily, as if from a shock of electricity. Not doubting that the contractions depended on the electric fluid, he at first suspected that they were connected with changes in the state of the atmosphere. He soon found, however, that this was not the case; and having varied, in many different ways, the circumstances in which the frogs were placed, he at length discovered that he could produce the movements at pleasure, by touching the animals with two different metals, which at the same time touched one another, either immediately, or by the intervention of some other substance capable of conducting electricity.
CHAP. II.
Of the Animals best fitted for Galvanic Experiments, of the Metals best calculated for making these Experiments, and of Conductors.
Almost every animal can be made to produce these muscular contractions by the Galvanic power, but those called cold blooded are the best. Thus frogs have been found the most convenient, both on account of their size and abundance. They also retain their muscular irritability to the Galvanic influence longer than most other animals, and it is asserted that strong convulsions can be produced in them many hours after the brain and spinal marrow have been destroyed; and also that when pretty far advanced in the process of putrefaction they are capable of Galvanic excitement.
No contractions have been produced in animals killed by corrosive sublimate, nor in those which have been starved to death: but a very slight motion can be made to appear in those killed by opium, the electric shock, or azotic gas.