Part 31

The substances of which the food of man is composed may be divided into two classes--into nitrogenised and non-nitrogenised. The former are capable of conversion into blood, the latter incapable of this transformation. Out of those substances which are adapted to the formation of blood are formed all the organised tissues. The other class of substances in the normal state of health serve to support the process of respiration. The former may be called the plastic elements of nutrition; the latter, elements of respiration.

Among the former we may reckon--vegetable fibrine, vegetable albumen, vegetable casein, animal flesh, animal blood.

Among the elements of respiration in our food are--fat, starch, gum, cane sugar, grape-sugar, sugar of milk, pectine, bassorine, wine, beer, spirits.

The nitrogenised constituents of vegetable food have a composition identical with that of the constituents of the blood.

No nitrogenised compound the composition of which differs from that of fibrine, albumen, and casein, is capable of supporting the vital process in animals.

The animal organism undoubtedly possesses the power of forming from the constituents of its blood the substance of its membranes and cellular tissue, of the nerves and brain, of the organic part of cartilages and bones. But the blood must be supplied to it ready in everything but its form--that is, in its chemical composition. If this is not done, a period is put to the formation of blood, and, consequently, to life.

The whole life of animals consists of a conflict between chemical forces and the vital power. In the normal state of the body of an adult these stand in equilibrium: that is, there is equilibrium between the manifestations of the causes of waste and the causes of supply. Every mechanical or chemical agency which disturbs the restoration of this equilibrium is a cause of disease.

Death is that condition in which chemical or mechanical powers gain the ascendancy, and all resistance on the part of the vital force ceases. This resistance never entirely departs from living tissues during life. Such deficiency in resistance is, in fact, a deficiency in resistance to the action of the oxygen of the atmosphere.

Disease occurs when the sum of vital force, which tends to neutralise all causes of disturbance, is weaker than the acting cause of disturbance.

Should there be formed in the diseased parts, in consequence of the change of matter, from the elements of the blood or of the tissue, new products which the neighbouring parts cannot employ for their own vital functions; should the surrounding parts, moreover, be unable to convey these products to other parts where they may undergo transformation, then these new products will suffer, at the place where they have been formed, a process of decomposition analogous to putrefaction.

In certain cases, medicine removes these diseased conditions by exciting in the vicinity of the diseased part, or in any convenient situation, an artificial diseased state (as by blisters), thus diminishing by means of artificial disturbance the resistance offered to the external causes of change in these parts by the vital force. The physician succeeds in putting an end to the original diseased condition when the disturbance artificially excited (or the diminution of resistance in another part) exceeds in amount the diseased state to be overcome.

The accelerated change of matter and the elevated temperature in the diseased part show that the resistance offered by the vital force to the action of oxygen is feebler than in the healthy state. But this resistance only ceases entirely when death takes place. By the artificial diminution of resistance in another part, the resistance in the diseased organ is not, indeed, directly strengthened; but the chemical action, the cause of the change of matter, is diminished in the diseased part, being directed to another part, where the physician has succeeded in producing a still more feeble resistance to the change of matter, to the action of oxygen.

SIR CHARLES LYELL

The Principles of Geology

Sir Charles Lyell, the distinguished geologist, was born at Kinnordy, Forfarshire, Scotland, Nov. 14, 1797. It was at Oxford that his scientific interest was first aroused, and after taking an M.A. degree in 1821 he continued his scientific studies, becoming an active member of the Geological and Linnæan Societies of London. In 1826 he was elected a fellow of the Royal Society, and two years later went with Sir Roderick Murchison on a tour of Europe, and gathered evidence for the theory of geological uniformity which he afterwards promulgated. In 1830 he published his great work, "Principles of Geology: Being an Attempt to Explain the Former Changes of the Earth's Surface by References to Causes now in Action," which converted almost the whole geological world to the doctrine of uniformitarianism, and may be considered the foundation of modern geology. Lyell died in London on February 22, 1875. Besides his great work, he also published "The Elements of Geology," "The Antiquity of Man," "Travels in North America," and "The Student's Elements of Geology."

I.--Uniformity in Geological Development

According to the speculations of some writers, there have been in the past history of the planet alternate periods of tranquillity and convulsion, the former enduring for ages, and resembling the state of things now experienced by man; the other brief, transient, and paroxysmal, giving rise to new mountains, seas, and valleys, annihilating one set of organic beings, and ushering in the creation of another. These theories, however, are not borne out by a fair interpretation of geological monuments; but, on the contrary, nature indicates no such cataclysms, but rather progressive uniformity.

Igneous rocks have been supposed to afford evidence of ancient paroxysms of nature, but we cannot consider igneous rocks proof of any exceptional paroxysms. Rather, we find ourselves compelled to regard igneous rocks as an aggregate effect of innumerable eruptions, of various degrees of violence, at various times, and to consider mountain chains as the accumulative results of these eruptions. The incumbent crust of the earth is never allowed to attain that strength and coherence which would be necessary in order to allow the volcanic force to accumulate and form an explosive charge capable of producing a grand paroxysmal eruption. The subterranean power, on the contrary, displays, even in its most energetic efforts, an intermittent and mitigated intensity. There are no proofs that the igneous rocks were produced more abundantly at remote periods.

Nor can we find proof of catastrophic discontinuity when we examine fossil plants and fossil animals. On the contrary, we find a progressive development of organic life at successive geological periods.

In Palæozoic strata the entire want of plants of the most complex organisation is very striking, for not a single dicotyledonous angiosperm has yet been found, and only one undoubted monocotyledon. In Secondary, or Mesozoic, times, palms and some other monocotyledons appeared; but not till the Upper Cretaceous era do we meet with the principal classes and orders of the vegetable kingdom as now known. Through the Tertiary ages the forms were perpetually changing, but always becoming more and more like, generically and specifically, to those now in being. On the whole, therefore, we find progressive development of plant life in the course of the ages.

In the case of animal life, progression is equally evident. Palæontological research leads to the conclusion that the invertebrate animals flourished before the vertebrate, and that in the latter class fish, reptiles, birds, and mammalia made their appearance in a chronological order analogous to that in which they would be arranged zoologically according to an advancing scale of perfection in their organisation. In regard to the mammalia themselves, they have been divided by Professor Owen into four sub-classes by reference to modifications of their brain. The two lowest are met with in the Secondary strata. The next in grade is found in Tertiary strata. And the highest of all, of which man is the sole representative, has not yet been detected in deposits older than the Post-Tertiary.

It is true that in passing from the older to the newer members of the Tertiary system we meet with many chasms, but none which separate entirely, by a broad line of demarcation, one state of the organic world from another. There are no signs of an abrupt termination of one fauna and flora, and the starting into life of new and wholly distinct forms. Although we are far from being able to demonstrate geologically an insensible transition from the Eocene to the Miocene, or even from the latter to the recent fauna, yet the more we enlarge and perfect our general survey the more nearly do we approximate to such a continuous series, and the more gradually are we conducted from times when many of the genera and nearly all the species were extinct to those in which scarcely a single species flourished which we do not know to exist at present. We must remember, too, that many gaps in animal and floral life were due to ordinary climatic and geological factors. We could, under no circumstances, expect to meet with a complete ascending series.

The great vicissitudes in climate which the earth undoubtedly experienced, as shown by geological records, have been held to be themselves proof of sudden violent revolutions in the life-history of the world. But all the great climatic vicissitudes can be accounted for by the action of factors still, in operation--subsidences and elevations of land, alterations in the relative proportions and position of land and water, variations in the relative position of our planet to the sun and other heavenly bodies.

Altogether, the conclusion is inevitable that from the remotest period there has been one uniform and continuous system of change in the animate and inanimate world, and accordingly every fact collected respecting the factors at present at work in forming and changing the world, affords a key to the interpretation of its part. And thus, although we are mere sojourners on the surface of the planet, chained to a mere point in space, enduring but for a moment of time, the human mind is enabled not only to number worlds beyond the unassisted ken of mortal eye, but to trace the events of indefinite ages before the creation of our race, and to penetrate into the dark secrets of the ocean and the heart of the solid globe.

II.--Changes in the Inorganic World now in Progress

The great agents of change in the inorganic world may be divided into two principal classes--the aqueous and the igneous. To the aqueous belong rain, rivers, springs, currents, and tides, and the action of frost and snow; to the igneous, volcanoes and earthquakes. Both these classes are instruments of degradation as well as of reproduction. But they may also be regarded as antagonist forces, since the aqueous agents are incessantly labouring to reduce the inequalities of the earth's surface to a level; while the igneous are equally active in restoring the unevenness of the external crust, partly by heaping up new matter in certain localities, and partly by depressing one portion of the earth's envelope and forcing out another.

We will treat in the first place of the aqueous agents.

RAIN AND RIVERS. When one considers that in some parts of the world as much as 500 or 600 inches of rain may fall annually, it is easy to believe that rain qua rain may be a denuding and plastic agent, and in some parts of the world we find evidence of its action in earth pillars or pyramids. The best example of earth pillars is seen near Botzen, in the Tyrol, where there are hundreds of columns of indurated mud, varying in height from 20 feet to 100 feet. These columns are usually capped by a single stone, and have been separated by rain from the terrace of which they once formed a part.