As in some degree illustrative of the pheno mena of animal electricity,properly so called, we must here take notice of the maniftstat ion of common electricity in animal substances and in living animals.
The mere contact of heterogeneous bodies is sufficient for the development of electricity; and animal tissues of dissimilar natures, both living and dead, obey the same law as other sub stances in this respect. For instance, a kind of voltaic pile has been formed by building up layers of muscle and nerve placed one above the other alternately; (Buntzen :) also by placing one upon another alternate layers of muscular fibre and brain, separated by a porous substance, soaked in salt-water. (Lagrave.) Another such has been made with plates of one kind of metal, fresh muscle, and salt-water, or blood, which acted on the galvanometer. When the con ductors of a galvanometer (Schweigger's) are armed with plates of platina, on one of which a piece of muscle of a few ounces in weight is placed, and the conductors are then plunged in blood or in a weak solution of salt, a deviation of the magnetic needle of the in strument is perceptible. (Prevost and Dumas.) The same happens when to one conductor is applied a plate of platina moistened with mu riate of antimony or nitric acid, to the other a piece of nerve, muscle, or brain, and both are brought into contact. (Majendie.) Dry piles of considerable electrical power may be formed of organic materials alone, without the interven tion of metals. If concentrated extracts of organic bodies (animal or vegetable) be spread upon thin paper, and piles be built up of discs cut from this paper, so that two dissimilar layers be separated by two thicknesses of the paper, so much electricity is developed that the elec trometer is affected. (Kcemtz.) When two persons, both insulated, join hands, electricity is developed sufficiently to affect Coulomb's electroscope. And, if the contraction of mus cles, the nervous connexion of which with the living body has been destroyed, be considered as a proof that they are subject to the influence of electricity, there are numerous experiments on record tending to prove that electricity is evolved by the mere contact of two dissimilar animal substances. Galvani, Volta, Humboldt, Aldini, Kellie, and Muller, have all found that when the muscles and the great nerves of a frog's limb are touched synchronously with a piece of the muscle of a warm-blooded animal, weak contractions of the frog's muscles ensue; and that, when the crural muscles are cut and folded back so as to touch the lumbar nerves, muscular contractions are perceived in the lower part of the limb. Aldini excited most powerful contractions by bringing the nerves of a warm blooded animal into contact with the muscles of a cold-blooded animal, and vice versa. And Muller has further found that contractions are excited by touching the moistened skin of the leg with the nerves of the thigh dissected out and turned down upon them ; the nerves being held by means of an insulating rod.* Tiedemann thus states the general results of experiments such as these. "1. The nerves of the muscles in which it is proposed to excite convulsions must make part of the chain. 2. The nerve or portion of nerve which is to make part of the chain must be isolated as completely as may be, and no other conductor must produce derivation in this portion of the chain, so as to oblige the electric current, when developed in the chain, to take a course through the nerves. 3. Cceteris paribus, the convulsions
are so much stronger, and are manifested over a greater extent, as the nervous portion, acting as a conductor, enters into the chain. 4. The convulsions are so much more powerful, and last the longer, as the chain is quickly formed, and the surface with which the parts consti tuting it are in contact is extensive." And lastly, we now know that even the evaporation of fluids, and changes in the molecular consti tution of both solids and fluids are always accompanied by electrical excitation.
Applying these facts to our knowledge of the various processes of the animal ceconomy, we cannot but conclude that, in the course of the many interchanges that are constantly taking place amongst the component particles of all living organs, electricity (perhaps modified by the organic forces) must be developed alto gether independently of nervous influence. It is certain, however, that electricity flowing from this source is very feebly manifested; at least it affects our best electrometers in a very incon siderable degree. Saussure frequently ex amined the electricity of his own body by means of Volta's electrometer, used along with a condenser, but always failed to perceive any indications of free electricity while he was entirely naked. It was also imperceptible while he perspired freely, and when his clothing was cold. Under other circumstances, he found the electricity of his body sometimes positive, and at other times negative; hut he could not determine the causes of these variations. Simi lar observations were made by Hemmer of Mannheim in 1186, both on the electricity of his own body, and on that of many other indi viduals placed in various circumstances. He obtained the following results. I. Electricity is developed in all men, but varies in intensity and in nature in different individuals. 2. The character and intensity of the electricity fre quently varies in the same person. In 2422 experiments, it was 1252 times positive, 771 negative, and 399 times imperceptible. 3. When the body is at rest and warm, its electricity is always positive. 4. When the surface is much cooled, the electricity becomes negative. 5. It is also negative when the muscular vigour is diminished. More recently this subject has been investigated by Messrs. Pfaff and Ahrens:I They used a gold-leaf electrometer; and the subjects of their observations were insulated. The collecting plate screwed on the electrometer was touched by the person experimented upon. The upper plate of the same was placed in communication with the ground by means of conductors. The results which they thus pro cured were as follows :-1. The electricity of healthy men is generally positive. 2. Irritable men of sanguine temperament have more free electricity than those of a phlegmatic tempera m•nt. a. An increased accumulation of elec tricity takes place in the evening. 4. Spirituous drinks augment its intensity. 5. The elec tricity of women is more frequently negative than that of men. 6. I n winter, while the body is very cold, no electricity is manifested, but it gradually reappears as the body is warmed. 7. The whole body naked, as well as every part of it, slims the same phenomena. ft. During the existence of rheumatism, the electricity is greatly diminished in intensity, but as the dis ease declines it again increases. Gardini found that the electricity of women during menstrua tion and pregnancy is negative.