these beings; yet they traverse the water with rapidity, without the aid of limbs or fins; and though many species are destitute of eyes, yet all possess an accurate perception of the presence of other bodies, and pursue and capture their prey with unerring purpose."

Among the most singular and important of the facts connected with this minute race of animals, is the existence in certain species of a case, shell, or shield, composed of lime, flint, or iron. These are indestructible, and remain after the animal has perished, forming immense beds, in the same way in which are sometimes found large collections of the remains of shell-fish. "From the inconceivable number of these shell-animalcules, which swarm in every body of water, whether fresh or salt, and the immense rapidity with which the species increase, extensive deposits or strata of their cases are constantly forming at the bottom of lakes, rivers, and seas. Hence have originated the layers of white calcareous earth common in peat-bogs and morasses; the tripoli or polishing slate of Bilin consisting wholly of the siliceous cases of animalcules, and the bog iron composed of ferruginous shields of other forms." The wonderful minuteness of these animals is shown by the fact that a cubic inch of the stone contains forty-one billions (41,000,000,000) of distinct organisms. The minuteness of the animalcules composing a kind of ochre, is stated to be even more extraordinary - a cubic inch containing no less than a trillion of them (1,000,000,000,000.)

Their prolific nature is no less remarkable than their size. Such is the rapidity with which they multiply that in one species a single individual may in four weeks have descendants to the amount of 268,435,456; and, according to Ehrenberg, some species are so fertile that 140,000,000 may proceed in four days from a single germ.

This completes a view of the whole animal kingdom, beginning with man, the most perfect member of it, and descending to those obscure and minute creatures which are only visible with the assistance of the microscope. It will be observed that one

common plan pervades the whole; that the same general objects are had in view in the structure of all, and that there is a general analogy in the methods employed for effecting these objects, although there is a great variety in the details; that there is a grand simplicity in the design, though a great diversity in the means. In short, not only in the structure of each individual animal, but in the wonderful manner in which the structure is varied to correspond to the nature, habits, and wants of the different classes, we may perceive the power, the wisdom, and the goodness of that great Creator, who has devised and formed, and who continues to sustain, the myriads of animated beings with which the earth is filled.

THE PHILOSOPHY

OF

NATURAL HISTORY.

CHAPTER I. (W.)*

OF THE FOOD, DIGESTION, AND BLOOD OF ANIMALS.

A GENERAL view of the several functions that subserve the purposes of animal life has already been given in the Introduc tion; but there are many other circumstances relating to them which still remain to be considered.

The form of the face and head, the general structure and proportions of the body and limbs, the means of attack and defence, the strength, agility, and speed of an animal, all correspond to the organs of digestion, and bear a definite relation to them, and to the kind of food.

Man cannot seize his food with his mouth, for his lips and teeth are upon a plane with the general surface of his face; but he has hands by which he conveys it there. In other animals, just in proportion as the hands or fore feet become less adapted to this purpose, the mouth, face, and teeth become projecting, so as to make up for the deficiency. Thus the hands of the monkey are less perfect than ours, but his face is more protuberant. The Carnivora have jaws of more power, and hands again of less, whilst in the hoofed animals - as the horse, and ox the jaws

* In the subsequent parts of this work, the chapters which are taken chiefly from the original publication of Smellie are denoted by S., and in these the passages substituted or added in the present edition are distinguished by a single inverted comma. The chapters prepared chiefly by the Editor are denoted by W., and the passages retained from the original are distinguished in the same way.

become very protuberant, and the fore feet are merely adapted for motion. This gradation in structure is also connected with the kind of food. Where an animal, as a hoofed quadruped, feeds upon substances firmly fixed to the earth, the mouth and teeth are sufficient. Where the food is not fixed, as flesh or fruit, something more is required. Hence animals living upon flesh, use their fore legs to hold down their prey while they tear it with their teeth; those living upon small fruits hold them between their fore feet, like the squirrel; whilst man and the monkeys, whose food is more various, have hands by which they can handle and prepare it.

Man is evidently capable of living, and does live, upon a great variety of food. But the question has been often discussed, whether his natural food be animal or vegetable? Is he, like most other animals, fitted by his nature to subsist upon a particular kind, or was he intended for that variety of diet, to which he has recourse? In his anatomical structure he is certainly most nearly allied to those species, such as the monkeys and their allied tribes, which in a state of nature live exclusively on fruits and vegetables. But experience shows that he is able to live, and enjoy at least equal health and strength, upon substances from the animal kingdom also. Some nations live exclusively on the one, some on the other; whilst the majority of mankind are addicted to the indiscriminate use of both. The tribes of Esquimaux, who inhabit the northern extremities of the earth, subsist entirely upon the flesh of whales, seals, walruses, bears, and fishes, never, except by accident, having the opportunity of tasting vegetable food. The Indians and Spaniards inhabiting some of the extensive plains of South America, frequented by immense droves of cattle, live almost exclusively upon beef. The Arabian supports himself on dried horseflesh, dates, and the milk and flesh of the camel; the millions of some of the regions of the East consume little else than rice; and the inhabitants of many portions of the tropical regions of the earth, subsist chiefly upon fruits and vegetables. Among the civilized nations of Europe and America, the tables of the better classes are spread with an immense variety from both kingdoms of Nature, whilst many of the poorer are limited to bread and vegetables.

Under all these different circumstances of diet, the average amount of health and strength does not seem, to common observation, to differ materially, so far as it is dependent on the kind of the food. Other circumstances appear to have more influence; such as the general mode of life, the occupation, the clothing, the habitations, and the quality and supply of air. It is probably true that if man have a sufficient quantity of aliment, and if his habits of life are well ordered in other respects, he may enjoy health, strength, and long life, upon all the kinds of food which have been mentioned. It is also true, however, that those tribes or classes of men whose situation enables them to gratify the appetite by a considerable variety, are more likely to attain to a high state of physical development, than those that are rigidly confined to a few articles.

The application of heat in the preparation of food undoubtedly contributes to the capacity for enduring this variety. Heat changes its texture and qualities; skilfully applied, it reduces very heterogeneous substances to a near approximation in their digestibility. Domestic animals whose food is cooked, resemble man in this respect. The dog and cat will subsist very well, and even exclusively, upon vegetable food, whilst, to some extent, though far less, some vegetable-eating animals will take animal food.

In fact there is not so great a difference between the products of the two kingdoms of Nature, used as food, as their sensible qualities would lead us to suppose. They consist essentially of the same principles. The vegetable world is the great laboratory in which food is prepared for the animal; and after its products have entered the bodies of animals, they are not greatly changed in their composition and essential qualities as articles for nutrition, though they are much altered from the texture and form in which they were swallowed.

The question then of the natural food of man is hardly capable of solution. It is as difficult to determine as that which relates to a supposed state of nature in other respects. Probably. there is, in the proper sense of the word, no absolute or uniform state of nature. Calculated for an extensive distribution over the surface of the earth, man has been endowed with a power of accommodating himself to great differences in country, climate,