CHAPTER X. THE EUROPEAN AGE OF REASON—(Continued). THE NATURE AND RELATIONS OF MAN. Position of Man according to the Heliocentric and Geocentric Theories. OF ANIMAL LIFE.-The transitory Nature of living Forms.-Relations of Plants and Animals.-Animals are Aggregates of Matter expending Force originally derived from the Sun. THE ORGANIC SERIES.-Man a Member of it.-His Position determined by Anatomical and Physiological Investigation of his Nervous System.— Its triple Forms: Automatic, Instinctive, Intellectual. The same progressive Development is seen in individual Man, in the entire animal Series, and in the Life of the Globe.—They are all under the Control of an eternal, universal, irresistible Law. The Aim of Nature is intellectual Development, and human Institutions must conform thereto. Summary of the Investigation of the Position of Man.--Production of Inorganic and Organic Forms by the Sun.-Nature of Animals and their Series.-Analogies and Differences between them and Man.-The Soul.-The World. man on the WHEN the ancient doctrine of the plurality of worlds was restored by Bruno, Galileo, and other modern The apparent astronomers, the resistance it encountered was position of mainly owing to its anticipated bearing on the heliocentric nature and relations of man. It was said, if theory. round our sun, as a centre, there revolve so many planetary bodies, experiencing the changes of summer and winter, day and night-bodies illuminated by satellites, and perhaps enjoying twilight and other benefits such as have been conferred on the earth-shall we not consider them the abodes of accountable, perhaps of sinful, beings like ourselves? Nay, more; if each of the innumerable fixed stars is, as our sun, a central focus of light, attended by dark and revolving globes, is it not necessary to admit that they also have their inhabitants? But among so many families of intelligent beings, how is it that we, the denizens of an insignificant speck, have alone been found worthy of God's regard? It was this reasoning that sustained the geocentric theory, and made the earth the centre of the universe, the most noble of created things; the sun, the moon, the stars, being only ministers for the service of man. But, like many other objections urged in that memorable conflict, this was founded on a misconception, There may The fallacy of objections or, rather, on imperfect knowledge. to that theory. be an infinity of worlds placed under the mechanical relations alluded to, but there may not be one among them that can be the abode of life. The physical conditions under which organization is possible are so numerous and so strictly limited that the chances are millions to one against their conjoint occurrence. Evidence In a religious point of view, we are greatly indebted to Geology for the light it has cast on this objecfurnished by tion. It has taught us that during inconceivable Geology. lapses of time our earth itself contained no living thing. These were those preorganic ages to which reference was made in the last chapter. Then by slow degrees, as a possibility for existence occurred, there gradually emerged one type after another. It is but as yesterday that the life of man could be maintained. The transitory living forms. Only in the presence of special physical conditions can an animal exist. Even then it is essentially nature of ephemeral. The life of it, as a whole, depends on the death of its integrant parts. In a waterfall, which maintains its place and appearance unchanged for many years, the constituent portions that have been precipitated headlong glide finally and for ever away. For the transitory matter to exhibit a permanent form, it is necessary that there should be a perpetual supply and also a perpetual removal. So long as the jutting ledge over which the waters rush, and the broken gulf below that receives them, remain unchanged, the cataract presents the same appearance. But variations in them mould it into a new shape; its colour changes with a clear or cloudy sky; the rainbow seen in its spray disappears when the beams of the sun are withdrawn. So in that collection of substance which constitutes an animal; whatever may be its position, high or low, in the realm of life, there is a perpetual introduction of new material and a perpetual departure of the old. It is a form, rather than an individual, that we see. Its permanence altogether depends on the permanence of the external conditions. If they change, it also changes, and a new form is the result. An animal is therefore a form through which material substance is visibly passing and suffering trans- Characterismutation into new products. In that act of tics of animal transmutation force is disengaged. That which life. we call its life is the display of the manner in which the force thus disengaged is expended. A scientific examination of animal life must include two primary facts. It must consider whence and Matter and in what manner the stream of material substance force. has been derived, in what manner and whither it passes away. And, since force can not be created from nothing, and is in its very nature indestructible, it must determine from what source that which is displayed by animals has been obtained, in what manner it is employed, and what disposal is made of it eventually. the sun. The force thus expended is originally derived from the sun. Plants are the intermedium for its con- Force is deveyance. The inorganic material of a saline na- rived from ture entering into their constitution is obtained from the soil in which they grow, as is also, for the most part, the water they require; but their organic substance is derived from the surrounding atmosphere, and hence it is strictly true that they are condensations from the air. These statements may be sufficiently illustrated, and the relation between plants and animals shown, by tracing the course of any one of the ingredients plants obtain entering into the vegetable composition, and de- material rived, as has been said, from the air. For this purpose, if we select their chief solid element, carbon, the remarks applicable to the course it follows will hold good for other accompanying elements. It is scarcely necessary Mode in which substance. Action of a plant on the air. to embarrass the brief exposition of vegetable life now to be given by any historical details, since these will come with more propriety subsequently. It is sufficient, to mention that the chemical explanations of vegetable physiology rest essentially on the discovery of oxygen gas by Priestley, of the constitution of carbonic acid by Lavoisier, and of water by Cavendish and Watt. While the sun is shining, the green parts of plants, especially the leaves, decompose carbonic acid, one of the ingredients of the atmospheric air. This substance is composed of two elements, carbon and oxygen; the former is appropriated by the plant, and enters into the composition of elaborated or descending sap, from which forthwith organic products, such as starch, sugar, wood fibre, acids, and bases are made. The other element, the oxygen, is for the most part refused by the plant, and returns to the air. As the process of decomposition goes on, new portions of carbonic acid are presented through mechanical movements, the trembling of the leaf, breezes, and currents rising from the foliage warmed by the solar beams giving place to other cool currents that set in below. The action of a plant upon the air is therefore the separation of combustible material from that medium. Carbon is thus obtained from carbonic acid; from water, hydrogen. Plant life is chemically an operation of reduction, for in like manner ammonia is decomposed into its constituents, which are nitrogen and hydrogen; and sulphuric and phosphoric acids, which like ammonia, may have been brought into the plant through its roots in the form of salt bodies, are made to yield up the oxygen with which they had been combined, and their sulphur and phosphorus, combustible elements, are appropriated. force. Every plant, from the humblest moss to the oak of a thousand years, is thus formed by the sun from Composition and resolution material obtained from the air-combustible of matter and material once united with oxygen, but now separated from that body. It is of especial importance to remark that in this act of decomposition, force, under the form of light, has disappeared, and become incorporated with the combustible, the organizing material This force is surrendered again, or reappears whenever the converse operation, combination with oxygen, occurs. Vegetable products thus constitute a magazine in which force is stored up and preserved for any assignable time. Hence they are adapted for animal food and for the procuring of warmth. The heat evolved in the combustion of coal in domestic economy was originally light from the sun appropriated by plants in the Secondary geological times, and locked for untold ages. up The sun is also the source from which was derived the light obtained in all our artificial operations of burning gas, oil, fat, wax, for the purposes of illumination. forces. My own experiments have proved that it is the light of the sun, in contradistinction to the heat, which Correlation occasions the decomposition of carbonic acid, of physical furnishing carbon to plants and oxygen to the atmosphere. But such is the relation of the so-called imponderable principles of chemistry to each other, and their mutual convertibility, that that which has disappeared in performing its function as light may reappear as heat or electricity, or in the production of some mechanical effect. Food is used by all animals for the sake of the force it thus contains, the remark applying to the car- The nature of nivora as well as the herbivora. In both cases food. the source of supply is the vegetable kingdom, indirectly or directly. The plant is thus indispensable to the animal. It is the collector and preserver of that force the expenditure of which constitutes the special display of animal life. From this point of view, animals must therefore be considered as machines, in which force obtained as has been described, is utilized. The food they take, or the tissue that has been formed from it, is acted upon by the air they breathe, and undergoes partial or total oxydation, and now emerges again, in part as heat in part as nerveforce, in some few instances in part as light or electricity, the force that originally came from the sun. and force There is, therefore, a cycle or revolution Cycle through through which material particles suitable for which matter organization incessantly run. At one moment pass. they exist as inorganic combinations in the air or the soil, |