Kitabı oku: «Omphalos: An Attempt to Untie the Geological Knot», sayfa 10

After a few months, the connexion of the now dead bone with the living is dissolved by absorption, and the horns fall off.

The next spring they are renewed again, but now with a branch or antler; and the whole falls again in autumn. Every spring sees them renewed, but always with an increase of development; and this increase is definite and well-known; so that the age of a Stag, at least of one in the vigour of life, can be readily and certainly stated.

For example, the individual Stag before us, now browsing so peacefully, has each horn composed of the following elements: – the beam, or main stem; two brow-antlers; one stem-antler, and a coronet of four snags, or royal-antlers, at the summit. This condition is peculiar to the seventh development, to which if we add one year for the hornless stage of fawnhood, we obtain eight years, as, beyond all doubt, the age of this Stag.

Both of these examples, however, the Ibex and the Stag, though so conclusive, and seemingly so irrefragable, are rendered nugatory by the opposing fact of a just recent creation.

See this Horse, a newly created, really wild Horse, his sleek coat of a dun mouse-colour, with a black stripe running down his back, and with a full black mane and tail. He has a wild spiteful glance; and his eye, and his lips now and then drawn back displaying his teeth, indicate no very amiable temper. Still, we want to look at those teeth of his. Please to moderate your rancour, generous Dobbin, and let us make an inspection of their condition!

 
"Wild as the wild deer, and untaught,
With spur and bridle undefiled," —
 

Now notice these peculiarities. The third pair of permanent incisors have appeared, and have attained the same level as their fellows; all are marked with a central hollow on the crown, the middle pair faintly: the canines have acquired considerable size; they present a regularly-convex surface outwardly, without any marks of grooving on the sides; their inner side is concave; their edges sharp; the third permanent molar has displaced its predecessor of the milk set, and the sixth is developed.⁸³

This condition of the teeth infallibly marks the fifth year of the Horse's age. A year ago the third incisor was only just rising; the canines were small, and strongly grooved, and the third milk grinder was yet existing. A year hence, the central incisors will be worn quite flat, and their marks obliterated; the canines will be fully grown tusks, the second molar will have reached its full height, and all the teeth will be of the same level. We can then with perfect confidence assert this to be a five-year old Horse. And yet, if we do so, we shall assert a palpable untruth, for the young and vigorous stallion has been created to-day.

In the thickets of this nutmeg grove beside us there is a Babiroussa; let us examine him. Here he is, almost submerged in this tepid pool. Gentle swine with the circular tusk, please to open your pretty mouth! Here are four incisors in the upper jaw; at one time there were six. The canines of the same jaw having pierced through the flesh and skin of the face, have grown upward and curved backward like horns; nay, they have nearly completed a circle, and are threatening to re-enter the skull; once these tusks had not broken from the gums. There are two pre-molars: once there were four. There are three molars, of which the first is worn quite smooth: once this surface was crowned with four cones; but the third molar had not then appeared.

Away to a broader river. Here wallows and riots the huge Hippopotamus. What can we make of his dentition? A strange array of teeth, indeed, is here; as uncouth and hideous a set as you may hope to see. Yes, but the group is instructive. We will take them in detail.

Look at the lower jaw first. Here are two large projecting incisors in the middle, with their tips worn away obliquely on the outer side, by the action of their opponents in the upper jaw, which are also worn inwardly. The outer incisors, both above and below, are also mutually worn in like manner. The lower canines form massive tusks, curved in the arc of a circle, ground away obliquely by the upper pair; which are short and similarly worn on their front edges. There are three pre-molars on each side, below and above, much worn: once there was a fourth, but it was shed early. Lastly, we find three molars, whose crowns are ground down so as to expose two polished areas of a four-lobed figure. A little while ago, these double areas were trilobate, but at first there were no smooth areas at all; for these are but sections, more or less advanced, of the conical knobs, with which the crown of the molar was originally armed.⁸⁴

In both these examples, the polished surfaces of the teeth, worn away by mutual action, afford striking evidence of the lapse of time. Some one may possibly object, however, to this: "What right have you to assume that these teeth were worn away at the moment of its creation, admitting the animal to have been created adult? May they not have been entire?" I reply, Impossible: the Hippopotamus's teeth would have been perfectly useless to him, except in the ground-down condition: nay, the unworn canines would have effectually prevented his jaws from closing, necessitating the keeping of the mouth wide open until the attrition was performed; long before which, of course, he would have starved. In a natural condition the mutual wearing begins as soon as the surface of the teeth come into contact with each other; that is, as soon as they have acquired a development which constitutes them fit for use. The degree of attrition is merely a question of time. There is no period that can be named, supposing the existence of the perfected teeth at all, in which the evidence of this action would not be visible. How distinct an evidence of past action, and yet, in the case of the created individual, how illusory!

 
"Trampling his path through wood and brake,
And canes, which, crackling, fall before his way,
And tassel-grass, whose silvery feathers play
O'ertopping the young trees, —
On comes the Elephant, to slake
His thirst at noon, in yon pellucid springs.
Lo! from his trunk upturn'd, aloft he flings
The grateful shower: and now
Plucking the broad-leaf'd bough
Of yonder plane, with waving motion slow,
Fanning the languid air,
He waves it to and fro."
 

We will not be content with admiring the vast size of the fine Dauntelah, and the majesty of his air and movement, and the intelligence manifested in all the actions of the "half-reasoning" beast, as he explores the amœnities of the young world to which he has but this morning been introduced. We are out on another sort of scent: let us try if we can glean any light from him on our present question.

And, first, we cannot fail to notice his fine pair of tusks curving upwards almost to a semicircle. Each tusk is composed of a vast number of thin cones of ivory, superimposed one on another; ever increasing by new ones formed within the interior at the base, and moulded upon the vascular pulp which fills the cavity, and by which the solid ivory is constantly secreted and deposited. Each new cone pushes further and further out those previously deposited, and thus the tusk ever grows in length as it increases in age.

How many years have these tusks occupied in attaining their present diameter and length? We cannot tell: without a transverse section we cannot determine the number of layers of which each consists: and if we could, we should yet require to know what ratio exists between the deposition of a cone of ivory and a fixed period of time. The cones, however, in a tusk of these dimensions, are very numerous, for they are but thin; and it is enough for our purpose that they have occupied the same number of periods of time for their formation, though we cannot precisely indicate the length of these periods.

Leaving the tusks, which are the upper incisors, let us now examine the molars. And there is in these a remarkable peculiarity of development, which will assist us greatly in our chronic inquiries. Before we look at them it may be as well to consider this peculiarity.

The Elephant has, from first to last, six, or perhaps eight, molars on each side of each jaw; but there are never more than two partially, or one wholly, in use at once. They have originally an uneven surface, produced by the extremities of a number of what may be considered as so many finger-like constituent teeth, arranged in transverse rows, covered by hard enamel, and cemented together by a bony substance. These points are gradually worn down by the process of mastication, and then the compound tooth appears crossed by narrow cartouches, or long ovals of enamel, indented at their margins.

"The first set of molars, [i. e. the first compound molar] or milk teeth, begins to cut the jaw eight or ten days after birth, and the grinders of the upper jaw appear before those of the lower one. These milk-grinders are not shed, but are gradually worn away during the time the second set are coming forward; and as soon as the body of the grinder is nearly worn away, the fangs begin to be absorbed. From the end of the second to the beginning of the sixth year, the third set come gradually forward as the jaw lengthens, not only to fill up this additional space, but also to supply the place of this second set, which are, during the same period, gradually worn away, and have their fangs absorbed. From the beginning of the sixth to the end of the ninth year, the fourth set of grinders come forward to supply the gradual waste of the third set. In this manner to the end of life, the Elephant obtains a set of new teeth, as the old ones become unfit for the mastication of its food.

"The milk-grinders consist each of four teeth, or laminæ; the second set of grinders of eight or nine laminæ; the third set of twelve or thirteen; the fourth set of fifteen, and so on to the seventh or eighth set, when each grinder consists of twenty-two or twenty-three: and it may be added, that each succeeding grinder takes at least a year more than its predecessor to be completed."⁸⁵

As each tooth advances, only a small portion pierces the gum at once; one of twelve or fourteen laminæ, for instance, shows only two or three of these through the gum, the remainder being as yet imbedded in the jaw; and in fact the tooth is complete at its fore part, where it is required for mastication, while behind it is still very incomplete; the laminæ are successively perfected as they advance. The molar of an Elephant can never, therefore, be seen in a perfect state: for if it is not worn in front, the back part is not fully formed and is without fangs; and when the structure of the hinder portion is perfected, the front part is already gone.

"When the complex molar cuts the gum, the cement is first rubbed off the digital summits; then their enamel cap is worn away, and the central dentine comes into play with a prominent enamel ring; the digital processes are next ground down to their common uniting base, and a transverse tract of dentine, with its wavy border of enamel, is exposed; finally, the transverse plates themselves are abraded to their common base of dentine, and a smooth and polished tract of that substance is produced. From this basis the roots of the molar are developed, and increase in length, to keep the worn crown on the grinding level, until the reproductive force is exhausted. When the whole extent of a grinder has thus successively come into play, its last part is reduced to a long fang supporting a smooth and polished field of dentine, with sometimes a few remnants of the bottom of the enamel folds at its hinder part. Then, having become useless, it is attacked by the absorbent action, by which, and the pressure of the succeeding tooth, it is finally shed."⁸⁶

With these physiological facts ascertained, let us proceed to the determination of the actual age of our noble Dauntelah. The molar in present use has a length of about nine inches, and a diameter of three and a half. Its crown is crossed by about eighteen enamel-plates; of which the anterior ones are much worn away, while the hinder ones can scarcely be counted with precision, as they have not wholly cut their way through the gum. These characters indicate the fifth molar (or set of molars) of the whole life-series. And the following facts will help us now to fix the actual age, at least approximately.

The first molar cuts the gum at two weeks old, is in full use at three months, and is shed in the course of the second year. The second cuts the gum at about six months, and is shed in the fifth year. The third appears at two years, is in full use about the fifth year, and finally disappears about the ninth year. In the sixth year the fourth breaks from the gum, and lasts till the animal's twenty-fifth year. The fifth cuts the gum at the twentieth year, is entirely exposed soon after the fortieth, and is thrust out about the sixtieth year, by the advance of the sixth molar, which appears at about fifty years old, and probably lasts for half a century more. If others succeed this, – a seventh and even an eighth, as some assert, – these would carry on the Elephant's life to two or three centuries, in accordance with an ancient opinion, which is in some degree countenanced by modern observations.

To come back, then, to the case before us, since the fifth molar has its fore part much worn, and the posterior laminæ scarcely yet protruded from the gum, it follows that this Elephant is now not far from the fortieth year of his life, a deduction which well agrees with the dimensions of his tusks, and his appearance of mature vigour.

Can you detect a flaw in this reasoning? And yet how baseless the conclusion, which assigns a past existence of forty years to a creature called into existence this very day.

X
PARALLELS AND PRECEDENTS

(Man.)

 
"Once, in the flight of ages past,
There lived a Man, – and who was he?
Mortal, howe'er thy lot be cast,
That man resembled thee." —
 

Montgomery.

We have knocked at the doors of the vegetable world, asking our questions; then at those of the lower tribes of the brute creation, and now at those of the higher forms; and we have received but one answer, – varying, indeed, in terms, but essentially the same in meaning, – from all. And now we have one more application to make; we have, still in our ideal peregrination, to seek out the newly-created form of our first progenitor, the primal Head of the Human Race.

And here we behold him; not like the beasts that perish, but —

 
"Of far nobler shape, erect and tall,
Godlike erect, with native honour clad,
In naked majesty, as lord of all."
 

The definitive question before us is this: Does the body of the Man just created present us with any evidences of a past existence, and if so, what are they? And that we may rightly judge of the matter, we will, as on former occasions, call in the aid of a skilful and experienced physiologist, to whom we will distinctly put the question.

The Physiologist's Report.

In replying to your inquiry concerning the proofs of a past existence in the Man before me, I must treat of him as a mere animal, – a creature having an organic being.

And, first, I find every part of the surface of his body possessing a nearly uniform temperature, which is higher than that of the surrounding atmosphere. There is, moreover, on all parts of the body, a tinge of redness, more or less vivid in certain regions. The heat, and the carnation tinge, alike indicate the presence of blood, arterial blood, diffused throughout, and, in particular, occupying the capillaries of the superficial parts. Every drop of this blood is preceded and succeeded by other drops, every one of which has been impelled out of the heart by its constant contractions.

But the very existence of this blood supposes the pre-existence of chyle and lymph, out of which it has been constructed. The chyle was formed out of chyme, changed by the action of the pancreatic and biliary secretions. Chyme is food, chemically altered by the action of the gastric juice. So that the blood, now coursing through the arteries and veins, implies the previous process of the reception of food. And these pancreatic and biliary secretions, which are essential to the conversion of chyme into chyle, – and therefore into blood, – do you ask their origin? They were prepared, the one by the pancreas, the other by the liver, from blood already existing, – blood previously formed of chyle with the addition of bile, &c. – and so indefinitely.

Again, the blood in these capillary arteries is of a bright scarlet hue, which it derives from its being charged with oxygen. This it received in the lungs, parting at the same time with the carbon which it had taken up in its former course. The lungs then must have existed before the blood could be where and what it is, viz. arterial blood in the capillaries of the extremities; before it was driven out of the heart, since it was transmitted from the lungs through the pulmonary veins into the heart, thence to be pumped into the arterial system.

But since all the tissues of the body are formed from the blood, the lungs were dependent on already-existing blood for their existence. And as the formative and nutrient power is lodged exclusively in arterial blood, the very blood out of which the lungs were organized was dependent on lungs for oxygenation, without which it would have been effete and useless.

Here then is a cycle of which I cannot trace the beginning.

But further. On the extremities of the fingers and of the toes, there are broad horny nails. These I trace down to the curved line where they issue from beneath the skin, and whence every particle of each nail has issued in succession. They are composed of several strata of polygonal cells, which have all grown in reduplications of the skin, forming compressed curved sheaths (follicles); stratum after stratum of cells having been added to the base-line, as the nail perpetually grew forwards. About three months elapse from the emergence of a given stratum of cells, before that stratum becomes terminal; and therefore each of these twenty-four finger- and toe-nails is a witness to three months' past existence.

The head is clothed with luxuriant hair, composed of a multitude of individual fibres, each of which is an epidermic appendage, essentially similar to the nails. Every hair is contained at its basal extremity in a delicate follicle, where it terminates around a soft vascular bulb, made up of blood-vessels and nerves. On the surface of this living bulb the horny substance is continually secreted and deposited in layers, each of which in succession pushes forward those previously made, till the tip extrudes from the follicle of the skin, after which it continues to grow in the same way, as an external hair. The tip is gradually worn away; and thus the constant growth cannot, in general, cause it to exceed a certain given length. Each of the thousands of hairs with which this majestic head is clothed, bears witness to past time; and as the increase of hair is about an inch per month, and as this hair is about four inches in length, we have here thousands of witnesses to at least four months of previous history.

The bones which make up the firm and stately fabric about which this human body is built, are no productions of a day. Long before this they existed in the form of cartilages. In these, minute arteries began to deposit particles of phosphate of lime, around certain centres of ossification, doing their work in a determinate order, and in regular lines, so as to form continuous fibres. These fibres, aggregated, and connected by others, soon formed a texture of spicula or thin plates.

Now take as an example a cylindrical hollow bone, as that of the thigh. Here the spicula were arranged longitudinally, parallel to the axis of the bone: preserving the general form of the cartilage which constituted its scaffolding.

But the bone required a progressive increase in size. In its early state, moreover, it was not hollow, but solid. Changes must have taken place to bring it to its present dimensions and condition. These were effected by the actual removal of some parts, simultaneously with the deposition of others.

At a certain stage of ossification, cells were excavated by the action of the absorbent vessels, which carried away portions of bony matter lying in the axis of the cylindrical bone. Their place was supplied by an oily matter, which is the marrow. As the growth proceeded, while new layers were deposited on the outside of the bone, and at the end of the long fibres, the internal layers near the centre were removed by the absorbent vessels, so that the cavity was further enlarged. In this manner the outermost layer of the young bone gradually changed its relative situation, becoming more and more deeply buried by the new layers which were successively deposited, and which covered and surrounded it; until by the removal of all the layers situated near to the centre, it became the innermost layer, and was itself destined in its turn to disappear, leaving the new bone without a single particle which had entered into the composition of the original structure.⁸⁷

These processes have been the slow and gradual work of years, of the lapse of which years the bones are themselves eloquent witnesses.

Within the mouth there are many teeth. I will not now speak of their exact number, nor of some other particulars concerning them, because I mean to return to them presently; but I look only at their general structure and origin. Each tooth consists of three distinct parts, the central portion, which is ivory; the exceedingly hard, polished, glassy coat of the crown, which is enamel; and a thin layer of bone around the fang, which is the cement.

Before either of these appeared, a minute papillary process of vascular pulp was formed in a cavity of the jaw. Over the pulp was spread an excessively thin membrane, which secreted from the blood, and deposited, a thin shell of bony matter, or ivory, moulded on the form of the pulp. Successive layers of ivory were then added, from within; the pulp diminishing in a corresponding ratio. The cavity of the jaw at the same time deepened, and the pulp lengthened downward into the space thus provided; layers of bony substance being gradually deposited upon it, as above.

The cavity itself was lined with a thick vascular membrane, united to the papilla at its base. Within the space lying between this membrane and the pulp, there was deposited from the wall of the former a soft, granular, non-vascular substance, known as the enamel organ. The cells on the inner surface of this substance then took the form of long, sub-parallel prisms, set in close array, perpendicular to the surface of the tooth. Earthy matter was progressively deposited in them, by which they became the exceedingly dense and hard enamel of the crown. The cement of the fang was then formed by a slight modification of the process which had produced the enamel.

Here, then, are several distinct and important processes, effected in regular and immutable succession, each requiring time for its performance, and all undeniably witnessed-to by the structure of every tooth here seen.

As I have thus proved the fact of life existing in this human body for some time previous to the present moment, I now proceed to inquire how far its structure may throw light on the actual duration of that past life. How far can we ascertain its chronology?

The stature of the Man before me is about six feet. An infant at birth is from eighteen to twenty-one inches in length. At ten years old the average stature is about four feet. Six feet may be taken as the full adult height of man; and this is attained from the twenty-first to the twenty-fifth year. The stature of this individual would therefore indicate an age not less than twenty-one years.

On the front of the throat I perceive a strongly-marked, angular prominence, formed by the union of the two plates of the thyroid cartilage. The prominence of this angle is due to the enlargement of the larynx; and it is accompanied by a deepening of the pitch of the voice, producing the full rich sounds that we have this instant heard, as the Man chanted his song of praise. These tones, and this projection of the thyroid cartilage, are equally distinctive marks of puberty, and do not appear till about the sixteenth or seventeenth year.

The chin, and sides of the face, are clothed with a dense bush of crisp hair, – the beard. This is a distinctive mark of the adolescent period, and may be taken as indicating an age not less than twenty years.

On again examining the mouth, I find the teeth are thirty-two in number; viz., four incisors, two canines, four pre-molars, and six true molars, in each jaw. None of these existed (at least visibly) during the first seven years of life; in that period they were represented by the milk-teeth of infancy. The appearance of the middle pair of incisors occurred at about the eighth year; the lateral incisors at nine; the first pre-molars at ten; the second at eleven; the canines at about twelve; the second molars at thirteen or fourteen; and the third molars, or dentes sapientiæ, at about seventeen or eighteen.

The state of the dentition, then, points to an age certainly not less than the period just named. How much more it may be, we must gather from other sources.

I come now to certain phenomena which are not appreciable to us on mere external examination; but which I am able with certainty to predicate. And the first of these is the proportion of arterial to venous blood in the capillaries. In infancy, the arterial capillaries contain far more blood than the capillary veins; in old age, the proportion is exactly reversed; whereas, in maturity, the ratio is just equal. Now, here there is a very small preponderance of arterial blood, indicating a period but slightly remote from maturity on the side of youth; well agreeing with the conclusion arrived at from previous premises, of some twenty to five-and-twenty years.

Other and more marked manifestations occur in the condition of the skeleton. In the spine, I find the spinous and transverse processes of the several vertebræ are completed by separate epiphyses, the ossification of which does not commence till after puberty, and the final union of which with the body of the bone does not occur till about the age of twenty-five years.

Each vertebra, moreover, has attained a smooth annular plate of solid bone, covering a surface that was previously rough and fissured, which is invariably added at the same period.

The ossification of the sacrum also has reached its culminating point. At the age of puberty, the component vertebræ began to unite from below upwards, and the two highest have now coalesced; which also marks a period of life not earlier than the twenty-fifth year. The whole united mass, moreover, is furnished on each side with thin bony plates, the appearance of which is no less characteristic of the same age.

Each of the ribs is here furnished with two epiphyses, one for the head and the other for the tubercle; the ossification of these began soon after puberty; but their union with the body of the bone, as presented here, has taken several years to accomplish.

To come to the limbs, we find the shoulder-blade presenting three epiphyses, one for the coracoid process, one for the acromion, and one for the lower angle of the bone, the ossification of which begins soon after puberty, their union with the body of the bone taking place between the ages of twenty-two and twenty-five years. The clavicle has an epiphysis at its sternal end, which begins to form between the eighteenth and twentieth years, and is united to the rest of the bone a few years later. The consolidation of the shoulder-bone (humerus) is completed rather earlier; the large piece at the upper end, which is formed by the coalescence of the ossific centres of the head and two tuberosities, unites with the shaft at about the twentieth year; whilst its lower extremity is completed by the junction of the external condyle, and of the two parts of the articulating surface (previously united with each other), at about the seventeenth year, and by that of the internal condyle in the year following. The superior epiphyses of the arm-bones (radius and ulna) unite with their respective shafts at about the age of puberty; the inferior, which are of larger size, at about the twentieth year. The epiphyses of the metacarpal and phalangeal bones (those of the hand and fingers) are united to their principals at about the twentieth year. In the Lower Extremities, the process of ossification is completed at nearly the same periods as that of the corresponding parts of the Upper. The consolidation of the hipbones (ilium, ischium, and pubis) to form the os innominatum, by the ossification of the triradiate cartilage that intervenes between them in the socket of the thigh (acetabulum), does not take place until after the period of puberty; and at this time additional epiphyses begin to make their appearance on the crest of the ilium, on its anterior inferior spine, on the tuberosity of the ischium, and on the inner margin of the pubes, which are not finally joined to the bone until about the twenty-fifth year.⁸⁸

The concurrence of these conditions in the skeleton, the nearly balanced ratio of the bloods, the perfected dentition, the beard, the deepened voice, the prominent larynx, and the stature, combine to point out, with infallible precision, the age of this Man, as between twenty-five and thirty years.

So far, then, we can with certainty trace back the history of this being, as an independent organism; but did his history then commence? O no; we can carry him much farther back than this. What means this curious depression in the centre of the abdomen, and the corrugated knob which occupies the cavity?⁸⁹