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HUMAN PHYSIOLOGY.

PROLEGOMENA.

I. NATURAL BODIES.

THE extensive domain of Nature is divisible into three great classes: -Minerals, Vegetables, and Animals. This division was universally adopted by the ancients, and still prevails, especially amongst the unscientific. When, however, we carefully examine their respective characteristics, we discover, that the animal and the vegetable resemble each other in many essential particulars. This resemblance has given occasion to the partition of all bodies into two classes: the Inorganic, or those not possessing organs or instruments adapted for the performance of special actions or functions, and the Organized, or such as possess this arrangement.

In all ages, philosophers have attempted to point out a

"Vast chain of being, which from God began,

Nature's ethereal, human, angel, man,

Beast, bird, fish, insect, what no eye can see,
No glass can reach-"

the links of which chain they have considered to be constituted of all natural bodies; passing by insensible gradations through the inorganic and the organized, and forming a rigid and unbroken series; and in which, they have conceived,

Each moss,

Each shell, each crawling insect, holds a rank,
Important in the plan of Him who framed
This scale of beings-holds a rank which, lost,
Would break the chain, and leave behind a gap
Which Nature's self would rue."

Crystallization has been esteemed by them as the highest link of the inorganic kingdom; the lichen, which encrusts the stone, as but one link higher than the stone itself; the mushroom and the coral as the connecting links between the vegetable and the animal; and the immense space, which separates man-the highest of the mammalia— from his Maker, they have conceived to be occupied in succession by beings of gradually increasing intelligence. If, however, we investigate the matter minutely, we discover that many links of the chain appear widely separated from each other; and that, in the existing

VOL. I.-3

state of our knowledge, the catenation cannot be esteemed rigidly maintained. Let us inquire into the great characteristics of the different kingdoms, and endeavour to describe the chief points in which living bodies differ from those that have never possessed vitality, and into the distinctions between organized bodies themselves.

1. DIFFERENCE BETWEEN INORGANIC AND ORGANIZED BODIES. Inorganic bodies possess the common properties of matter. Their elements are fixed under ordinary circumstances. Their study constitutes Physics, in its enlarged sense, or Natural Science. Organized bodies have properties in common with inorganic, but they have likewise others superadded, which control the first in a singular manner. They are beings, whose elements are undergoing constant mutation, and the sciences treating of their structure and functions are Anatomy and Physiology.

They differ from each other in

1. Origin.-Inorganic bodies are not born: they do not arise from a parent: they spring from the general forces of matter, the particles being merely in a state of aggregation, and their motions regulated by certain fixed and invariable laws. The animal and the vegetable, on the other hand, are products of generation; they must spring from beings similar to themselves; and they possess the force of life, which controls the ordinary forces of matter. Yet it has been supposed, that they are capable of creating life; in other words, that a particular organization presupposes life. This is not the place for entering into the question of generation. It will be sufficient at present to remark, that in the upper classes of animals, the necessity of a parent cannot be contested; the only difficulty that can possibly arise regards the very lowest classes; and analogy warrants the conclusion, that every living being must spring from an egg or a seed.

2. Shape. The shape of inorganic bodies is not fixed in a determinate manner. It is true, that by proper management every mineral can be reduced to a primitive nucleus, which is the same in all minerals of like composition; still, the shape of the mineral, as it presents itself to us, differs. Carbonate of lime, for example, although it may always be reduced to the same primitive nucleus, assumes various appearances; -being sometimes rhomboidal; at others, in regular hexahedral prisms; -in solids, terminated by twelve scalene triangles, or in dodecahedrons, whose surfaces are pentagons. In organized bodies, on the contrary, the shape is constant. Each animal and vegetable has the one that characterizes its species, so that no possible mistake can be indulged; and this applies not only to the whole body, but to every one of its parts, numerous as they are.

3. Size. The size of an inorganic body is by no means fixed. It may be great, or small, according to the quantity present of the particles that have to form it. A crystal, for example, may be minute, or the contrary, according to the number of saline particles in the solution. On the other hand, organized bodies attain a certain size,—at

[blocks in formation]

times by a slow, at others by a more rapid growth,—but in all cases the due proportion is preserved between the various parts,-between the stem and the root, the limb and the trunk. Each vegetable and each animal has its own size, by which it is known; and although we occasionally meet with dwarf or gigantic varieties, these are unfrequent, and mere exceptions, establishing the position.

4. Chemical character.-Great difference exists between inorganic and organized bodies in this respect. In the mineral kingdom are found all the elementary substances, or those which chemistry, at present, considers simple; amounting to at least sixty-three. They are as follows:-Non-metallic bodies. Oxygen, hydrogen, nitrogen, sulphur, selenium, phosphorus, chlorine, iodine, bromine, fluorine, carbon, boron, silicon. Metals. Potassium, sodium, lithium, calcium, magnesium, barium, strontium, aluminium, glucinium, zirconium, yttrium, thorium, iron, manganese, zinc, cadmium, lead, tin, copper, bismuth, mercury, silver, gold, platinum, rhodium, palladium, osmium, iridium, nickel, cobalt, uranium, cerium, antimony, arsenic, chromium, molybdenum, tungsten, columbium, tellurium, titanium, vanadium, lantanium, didymium, erbium, terbium, pelopium, niobium, ruthenium, norium, and ilmenium. In the organized, a few only of these elements of matter are met with, viz., oxygen, hydrogen, azote, carbon, sulphur, phosphorus, chlorine, fluorine, potassium, sodium, calcium, silicium, aluminium, iron, manganese, titanium, and arsenic.

The composition of inorganic bodies is more simple; several consist of but one element; and, when composed of more, the combination is rarely higher than ternary. Organized bodies, on the other hand, are never simple, nor even binary. They are always at least ternary or quaternary. The simplest vegetable consists of a union of oxygen, carbon, and hydrogen; the simplest animal, of oxygen, hydrogen, carbon, and nitrogen.

The composition of the mineral, again, is constant. Its elements have entirely satisfied their affinities; and all remains at rest. In the organized kingdom, the affinities are not satisfied; compounds are formed to be again decomposed; and this happens from the earliest period of foetal formation till the cessation of life: all is in commotion, and the chemical character of the corporeal fabric incessantly undergoing modification. This applies to every organized body; and, accordingly, change of some kind is essential to our idea of active life. In the case of the seed, which has remained unaltered for centuries, and subsequently vegetates under favourable circumstances, life may be considered to be dormant or suspended. It possesses vitality, or the power of being excited to active life under favouring influences.

In chemical nomenclature, the term element has a different acceptation, according as it is applied to inorganic or organic chemistry. In the former, it means a substance, which, in the present state of science, does not admit of decomposition. We say, "in the present state of the science," for several bodies, now esteemed compound, were, not many years ago, classed amongst the simple or elementary. It is not much more than thirty years since the alkalies were found to be composed of two elements. Previously, they were considered simple. In

the animal and the vegetable, we find substances, also called elements, but with the epithet organic prefixed, because they are only found in organized bodies; and are therefore the exclusive products of organization and life. For example, in both animals and vegetables we meet with oxygen, hydrogen, carbon, nitrogen, and different metallic substances: these are chemical or inorganic elements. We further meet with albumen, gelatin, fibrin, osmazome, &c., substances which constitute the various organs, and have, therefore, been termed organic elements or compounds of organization; yet they are capable of decomposition; and in one sense, therefore, not elementary.

In the inorganic body, all the elements, that constitute it, are formed by the agency of general chemical affinities; but, in the organized, the formation is produced by the force that presides over the formation of the organic elements themselves, the force of life. Hence, the chemist is able to recompose many inorganic bodies; whilst the products of organization and life set his art at defiance.

The different parts of an inorganic body enjoy an existence independent of each other; whilst those of the organized are materially dependent. No part can, indeed, be injured without the mass and the separated portion being more or less affected. If we take a piece of marble, which is composed of carbonic acid and lime, and break it into a thousand fragments, each portion will be found to consist of carbonic acid and lime. The mass will be destroyed; but the pieces will not suffer from the disjunction. They will continue as fixed and unmodified as at first. Not so with an organized body. If we tear the branch from a tree, the stem itself participates more or less in the injury; the detached branch speedily undergoes striking changes; it withers; becomes shrivelled; and, in the case of the succulent vegetable, undergoes decomposition; certain of its constituents, no longer held in control by vital agency, enter into new combinations, are given off in the form of gas, and the remainder sinks to earth.

Changes, no less impressive, occur in the animal when a limb is separated from the body. The parent trunk suffers; the system recoils at the first infliction of the injury, but subsequently arouses itself to a reparatory effort, at times with such energy as to destroy its own vitality. The separated limb, like the branch, is given up, uncontrolled, to new affinities; and putrefaction soon reduces the mass to a state in which its previously admirable organization is no longer perceptible. Some of the lower classes of animals may, indeed, be divided with impunity; and with no other effect than that of multiplying the animal in proportion to the number of sections; but these cases are exceptions; and we may regard the destructive process,-set up when parts of organized bodies are separated,-as one of the best modes of distinction between the inorganic and organized classes.

5. Texture. In this respect the inorganic and organized differ considerably, a difference which has given rise to their respective appellations. To the structure of the latter class only can the term texture be with propriety applied. If we examine a vegetable or animal substance with attention, we find, that it has a regular and determinate arrangement or structure; and readily discover, that it consists of va

rious parts; in the vegetable, of wood, bark, leaves, roots, flowers, &c.; and in the animal, of muscles, nerves, vessels, &c.; all of which appear to be instruments or organs for special purposes in the economy. Hence, the body is said to be organized, and the result, as well as the process, is often called organization. Properly, organization means the process by which an organized being is formed; organism, the result of such process, or organic structure.

The particles of matter in an organized body, in many instances, constitute fibres, which interlace and intersect each other in all directions, and form a spongy areolar texture or tissue, of which the various organs of the body are composed. These fibres, and indeed every organized structure, are considered by modern histologists to be formed. originally from cellgerms or cytoblasts: the resulting cells assuming an arrangement appropriate to the particular tissue. "A texture," says Mr. Goodsir," may be considered either by itself, or in connexion with the parts which usually accompany it. These subsidiary parts may be entirely removed without interfering with the anatomical constitution of the texture. It is essentially non-vascular;-neither vessels nor nerves entering into its intimate structure. It possesses in itself those powers by which it is nourished, produces its kind, and performs the actions for which it is destined, the subsidiary or superadded parts supplying it with materials, which it appropriates by its own inherent powers, or connecting it in sympathetic and harmonious action with other parts of the organism to which it belongs. In none of the textures are these characters more distinctly seen than in the osseous. A well-macerated bone is one of the most easily made, and at the same time one of the most curious of anatomical preparations. It is a perfect example of a texture completely isolated; the vessels, nerves, membranes, and fat, are all separated; and nothing is left but the nonvascular osseous substance.'

In the inorganic substance the mass is homogeneous; the smallest particle of marble consists of carbonic acid and lime; and all the particles concur alike in its formation and preservation.

Lastly, while an inorganic body, of a determinate species, has always a fixed composition, the living being, although constituting a particular species, may present individual differences, which give rise in the animal, to various temperaments, constitutions, &c.

6. Mode of preservation.-Preservation of the species is, in organized bodies, the effect of reproduction. As regards individual preservation, that of the mineral is dependent upon the same actions that effected its formation; on the persistence of the affinities of cohesion and combination that united its various particles. The animal and the vegetable, on the other hand, are maintained by a mechanism peculiar to themselves. From the bodies surrounding them they lay hold of nutritious matter, which, by a process of elaboration, they assimilate to their own composition; at the same time, they are constantly absorbing

Anatomical and Pathological Observations, p. 64, Edinburgh, 1845. See also Schwann, Microscopical Researches into the Accordance in the Structure and Growth of Animals and Plants; translated by Henry Smith. Sydenham Society edit. Lond. 1847.

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