54 AGENCY OF ELECTRICITY. parent to the egg, during her long and patient fidelity to her nest, elicits that response on the part of the germ, which leads on to the hatching of the chick. The seeds of plants stand in similar need of the solar warmth in order to germinate, and acknowledge it as promptly. So, indeed, with the gestation of viviparous animals, as woman. The embryo, embedded in the womb, amplifies into a fully-formed child, not more through the contributions made to its substance by the nutrient apparatus provided for the purpose, than through the agency of the genial warmth which flows into it from all sides, and without which neither limbs nor organs could be moulded. 25. What may be the precise way in which Electricity assists in maintaining life, is as yet a profound secret. From what has been observed, however, there cannot be a doubt that it performs a part fully as energetic as either light or heat, and this whether we take animals or plants. As regards the former, its peculiar relation appears to lie with "nerve-force." Nerve-force is excitable by electricity, and electricity may be produced by the exercise of nerve-force, as exemplified in those remarkable creatures, the Torpedo and the Gymnotus. Our personal sensations, which are an unfailing index to the truth in such inquiries, tell us how exhilarating is an atmosphere well charged with this magical element, and how life languishes when it is deficient or rendered inoperative. Plants receive a corresponding benefit. The evolution of new tissue is greatly accelerated by a plentiful supply of the electric fluid, manifesting itself in rapid and lively growth. For particulars respecting its agency, also concerning the relation of heat, light, and electricity, generally, to Organic life, we must refer the reader to treatises the scope of which allows more room than can be afforded here; giving what space remains to a notice of the grand discovery, so ably set forth by Mr. Grove, that in DOCTRINE OF THE "CORRELATION OF FORCES." 55 stead of being three things, Light, Heat, and Electricity are only one, variously set forth, and mutually convertible, the doctrine in short of the "Correlation of the Physical Forces." It is important briefly to consider this doctrine, seeing that it provides, in the estimation of some of the most eminent physiologists of our day, a solution of the great problem of organic life. "That Light and Heat," says Carpenter, "become transformed into Vital Force, is shown by the same kind of evidence that we possess of the conversion of Heat into Electricity by acting on a certain combination of metals; of Electricity into Magnetism by being passed round a bar of iron; and of Heat and Electricity into motion when the self-repulsive action separates the particles from each other. For just as Heat, Light, Chemical affinity, &c., are transformed into vital force, so is vital force capable of manifesting itself in the production of Light, Heat, Electricity, Chemical affinity, or mechanical motion; thus completing the proof of that mutual relationship or 'correlation' which has been shown to exist among the physical and chemical forces themselves." ""* That without heat and electricity, life cannot for one instant be sustained, is indisputable; and that without them, the changes and phenomena which disclose its presence can never occur. Equally true is it that (as specially observable in the Cerealia abovementioned) there is a definite relation between the degree of vital activity and the amount of heat, light, &c. supplied to the organism. Curious and truly wonderful too is the concord between these "forces" and the vital energy, as regards their restorative powers; the warmth of the hand restores the perishing fly, and the voltaic current reanimates the half-drowned man. To say, however, that they are trans * "Principles of Human Physiology," p. 123. 1853. See also the "Projet d'un Essai sur la Vitalité," of Andral, p. 35. Paris, 1835. 56 J. J. G. WILKINSON ON CORRELATION, formable into a spiritual essence-for if life be derived from God, vital force can be nothing else seems to savor strongly of such a perfect contentedness with the material as surely does not consist with a pure and devout philosophy. The dependence of life, proximately, upon physical causes, is not questioned; life is no miracle, in the special sense; and it is our plain and bounden duty, as investigators of nature, to attempt to give to this dependence a clear and definite expression. But we are not to talk of "vital force" as if it were a thing of merely terrestrial origin, heat and electricity sublimed and transmuted. "According to this doctrine of correlation "* (i. e., of the physical forces with vital force,) observes an author of no common sagacity, "according to this doctrine, heat has only to pass through a cell-germ to be converted into vitality. This doctrine ends, therefore, in fire-worshipping; for it makes the light and heat of the material sun, the fountains of the force of organization; and deems that these pass through vegetables, and become vegetable life; through animals, and become animal life; through brains, and become mind, and so forth. Therefore, a fine day, poured into its vessel, man, becomes transmogrified into virtues; dark nights are converted into felonies; dull November days into suicides; and hot suns into love. This is materialism with spiritualism in its pocket. There is no convertibility of forces between life and nature; there are no cells by which heat can be filtered into vitality."t *On the general subject of the Correlation of Forces see Mr. Grove's admirable work bearing that title, and an excellent article on the "Phasis of Force" in the National Review for April, 1857. "The Human Body, and its connection with Man," by J. J. Garth Wilkinson, p. 389. 1851. CHAPTER IV. FOOD. 26. WHEREVER provided with instruments of action, life requires for its maintenance unbroken supplies of food. No organized being can dispense with food altogether, though some, from peculiarity of constitution-as reptiles, the carnivorous mammalia, certain hybernating creatures, and trees-can fast for surprisingly long periods. Plants feed in order that they may enlarge their fabric, and renew, periodically, their foliage and blossoms; animals feed because the exercise of their various organs is attended by decomposition of their very substance, which consequently needs to be repaired to the same extent. While the lungs, the heart, the liver, the muscles, the nerves, perform faithfully the several duties assigned to or demanded of them, it is at the expense of the material they are composed of; and were the loss not speedily compensated, life would soon be necessitated to depart, as it actually does in cases of starvation. For life, in animals, is not merely living-it consists not alone in the activity and vigorous exercise of the bodily organs. In order to its energetic playing forth, there is needed a nice balance and alternation of death and renewal in every tissue concerned in the vital processes; and only where exchange of new for old is regularly and actively going on, can life be truly said to reign. We cannot live, in a word, as to our total organism, unless we are always dying as to our atoms; nor is there an instant in which death 58 MOLECULAR DEATH AND RENEWAL OF THE BODY. is not somewhere taking place. Every effort and every movement kills some portion of the muscles employed; every thought, even, involves the death of some particle of the brain. As fast as devitalized, the atoms are cast outsome through the lungs, others through the skin, &c.; every pore and passage of the body supplying means of exit. So general and incessant is the decomposition, and along with it the rebuilding, that a few weeks probably suffice for the dissolving and reconstruction of the entire structure; certainly it does not occupy many years. In the course of a life-time, "every individual wears out many suits of bodies, as he does many suits of clothes; the successive structures which we occupy bear the same name, and exhibit the same external aspect; but our frames of to-day are no more identical with the frames of our early youth than with those of our progenitors." In this wonderful flux and replacement of the atoms of the body, quite as much consists its admirable adaptation to the purposes of life as in its exquisite mechanism and variety of organs. It is so perfect an instrument of life, because composed of millions of delicate pieces, so slenderly cohering that any one of them can be discarded and replaced without difficulty. Hence, in the aged, and in the deceased, where the tissues are hardened and consolidated, where the renewal is slow, difficult, and irregular, we see life proportionately feeble; where, upon the other hand, they are soft and delicate, and renewal rapid, it is in the same ratio strong and beautiful. Historically viewed, the periodical renewal, of the human body at least, is one of the most venerable ideas in physiology. Long before Cuvier's fine comparison of the human fabric to a whirlpool, and Leibnitz's simile of a river, it had been likened to the famous ship of Theseus, which was always the same ship, though from being so often repaired, not a single piece of the original was left. Plato adverts to it both in the Ban |