On Molecular and Microscopic Science, Volume 2 (of 2)

SECTION I.. Functions of the Animal Frame.

FUNCTIONS OF THE ANIMAL FRAME.

ALTHOUGH animal life is only known to us as a manifestation of divine power not to be explained, yet the various phases of life, growth, and structure in animals, from the microscopic Monad to Man, are legitimate subjects of physical inquiry, being totally independent of those high moral and religious sentiments which are peculiar to Man alone.

The same simple elements chemically combined in definite but different proportions form the base of animal as well as of vegetable life. But besides the elementary gases and carbon, many substances, simple and compound, are found in the animal frame; the phosphate and carbonate of lime, iron which colours the blood, and common salt which, with the exception of water, is the only article of food we use in a mineral state. Animals derive their nourishment, both directly and indirectly, from vegetables. Their incapacity to change inert into living matter is one of the most characteristic distinctions between the animal and vegetable kingdoms.

Protoplasm was shown to be rudimentary formative vegetable matter: so Sarcode, or rudimentary flesh, forms the whole or part of every animal structure. It is a semi-fluid substance, consisting of an albuminous base, mixed with particles of oil in a state of very fine division. It is tenacious, extensile, contractile, and diaphanous, reflecting light more than water, but less than oil. It is rendered perfectly transparent by citric acid, and is dyed brown by iodine. This substance, in a homogeneous state, constitutes the whole frame of the lowest grade of animal life; but when gradually differentiated into cell-wall and cell-contents, it becomes the origin of animal structure from that which has little more than mere existence to man himself; in fact, cellular origin and cellular structure prevail throughout every class of animal life. Unicellular plants and animals live for themselves independently and alone; but the cells which form part of the higher and compound individuals of both kingdoms, may be said to have two lives, one peculiarly their own, and another depending on that of the organized beings of which they form a part.

Flesh or muscle, which is organized sarcode, consists of two parts, namely, bundles of muscular fibre imbedded in areolar tissue. Nervous matter also consists of two parts, differing much in appearance and structure, the one being cellular, the other fibrous. The vital activity of the nerves far surpasses that of every other tissue; but there is an inherent irritability in muscular fibre altogether independent of nervous action: both the nervous and muscular tissues are subject to decay and waste.

The blood, which is the ultimate result of the assimilation of the food and respiration, conveys nourishment to all the tissues during its circulation; for with every breath, with every effort, muscular or mental, with every motion, voluntary or involuntary, at every instant of life, asleep or awake, part of the muscular and nervous substances becomes dead, separates from the living part, is returned to the circulation, combines with the oxygen of the blood, and is removed from the system, the waste being ordinarily in exact proportion to the exertion, mental and physical. Hence food, assimilated into blood, is necessary to supply nourishment to the muscles, and to restore strength to the nervous system, on which all our vital motions depend; for, by the nerves, volition acts upon living matter. Waste and repair is a law of nature, but when nature begins to decay, the waste exceeds the supply.

However, something more than food is necessary, for the oxygen in the blood would soon be exhausted were it not constantly restored by inspiration of atmospheric air. The perpetual combination of the oxygen of the air with the carbon of the blood derived from the food is a real combustion, and the cause of animal heat; but if the carbonic acid gas produced by that chemical union were not continually given out by the respiratory organs, it would become injurious to the animal system. Thus respiration and the circulation of the blood are mutually dependent; the activity of the one is exactly proportional to that of the other: both are increased by exercise and nervous excitement.

External heat is no less essential to animals than to vegetables; the development of a germ or egg is as dependent on heat as that of a seed. The amount of heat generated by respiration and that carried off by the air is a more or less constant quantity; hence, in hot countries, rice and other vegetable diet is sufficient, but as the cold increases with the latitude, more and more animal food or hydrocarbon is requisite for the production of heat.

The waste of the tissues, and the aëration of the vital juices, that is, the exchange of the respiratory gases, are common to all animals. The heart, upon whose expansions and contractions the circulation of the blood depends, is represented in the lower animals by propelling organs of a variety of forms; and the organs of respiration differ exceedingly, according to the medium in which the animals live. Water, both fresh and salt, though a suffocating element to land animals, contains a great deal of air, not only in the state of gas, but also in solution, the quantity in solution being directly as the pressure; so that animals living in the deepest recesses of the ocean breathe as freely as those that live on land, but with respiratory organs of a very different structure. In the lowest classes, which have no respiratory organs at all, the gases are exchanged through their thin delicate skins.

The mechanical forces act within the living being according to the same laws as they do in the external world: the chemical powers too, which are the cause of digestion, heat, and respiration, follow the same laws of definite and quantitative proportion as they do in inert matter; but neither the mechanical forces, nor the physical powers, could create a germ; nor could they even awaken its dormant state to living energy, unless a vital power existed in it, the origin of which is beyond the reach of man.

Animals are endowed with nerve-force, in addition to mechanical force and the physical powers which are common to them and vegetables; a force which constitutes their prime distinction, which is superior to all the other powers from its immediate connection with mind, and which becomes more evident, and more evidently under the control of the animal, in proportion as the animal approaches the higher grades of life, and only attains its perfect development in the human race.

The bones of man and the higher animals are clothed with a system of muscles, so attached that the head, eyes, limbs, &c., can be moved in various directions. In each of these muscles the fibres of two sets of nerves ramify, namely, the sensory and the motor nerves.

The sensory nerves convey external impressions to the brain, and by them alone the mind is rendered conscious of external objects. The impressions made by light and sound upon the eye and the ear, or by mechanical touch on the body, are conveyed by the sensory nerves to the brain, where they are perceived, though the impressions take place at a distance from it. Conversely, the mind or will acts through the brain on the motor nerves, which by alternately contracting, relaxing, and directing the muscles, produces muscular motion. Thus the motor nerves convey the emotions of the mind to the external world, and the sensory nerves convey the impressions made by the external world to the mind. By these admirable discoveries, Sir Charles Bell has proved that ‘we are placed between two worlds, the invisible and the material;’ our nervous system is the bond of connection. The connection, however, between the mind and the brain is unknown: it has never been explained, and is probably inexplicable; yet it is evident that the mind or will, though immaterial, manifests itself by acting on matter; that is, as a power which stimulates the nerves, the nerve-force acting on the muscles. Mental excitement calls forth the most powerful muscular strength, and an iron will can resist the greatest nervous excitement. The nervous and muscular forces are perpetually called into action, because, for distinct perception, the muscles require to be adjusted. Mind is passive as well as active: we may see an object without perceiving it, and we may hear a sound without attending to it. We must look in order to see, listen in order to hear, and handle in order to feel; that is, we must adjust the muscular apparatus of all our senses, of our eyes, ears, &c., if we would have a distinct perception of external exciting objects: and that is accomplished by the power of mind acting upon matter.

Dr. Carpenter has shown that it is by a series of forces acting upon matter that man conveys his ideas to man, the sonorous undulations of the atmosphere being the medium between the two. On one side the will, or power of mind, acts upon the nerves, nerve-force acts upon the muscles of speech, and these muscles, while in the act of speaking, produce sonorous undulations in the atmosphere. On the other side, these undulations are communicated by the mechanism of the ear to the auditory nerves, exciting nerve-force, and nerve-force acts upon the mind of the hearer. ‘Thus the consciousness of the speaker acts upon the consciousness of the hearer by a well-connected series of powers.’

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