To the imagination of man, magnitude presents itself as one of the noblest and most impressive attributes with which material objects are clothed.' The colossal grandeur of the Alps, amid the wonders of nature, or of the Pyramids among the master-pieces of art, affects the sensuous nature of the beholder with unmingled reverence and awe. But the refined intelligence seeks for a higher standard of value than size can afford. Sense bows before the majesty of sublime proportion; reason first seeks to investigate all the relations of material things, and, in the end, exalts to the highest place those which a searching test has declared to possess the loftiest significance. Not unfrequently it is seen that forms the most minute are most essential. They were the Titanic forces and grander features of nature which evoked the admiration and the worship of the earliest tribes of men. As we descend along the stream of time, we may discover a growing perception of the greatness of small things; the marvellous power of minor organisms to work immeasurable changes, and the exquisite beauty of minute structures.

Many centuries ago, thoughtful men foreshadowed the full expression of this ripening truth, and anticipated the results of modern science in a profound axiom - tota natura in minimis - in smallest things is nature greatest. It was reserved for this century to develop a saying of the schools into a household precept. This age has cast down barriers that walled round the human vision, and has' spread out before us a whole universe of created things, of which no man knew before our time. We see now, by the aid of the microscope, that greatness has no existence but as composed of infinite littleness. Who that bowed before the oak could have thought the lord of the forest to be a compound mass of many millions of independent organisms, of which thousands are combined within an acorn f Who that looked upon the mountain chains of Western Asia, or the white cliffs of Dover, could surmise that they were the handiwork of infusorial animalcules, whose shells make up the mass in numbers of thirty millions to a cubic inch? These are the revelations of the microscope.

Gifted with this new power, the naturalist has traversed the material universe as though armed with a magician's wand; and beneath all diverse shapes, amid all various structures, he has found one simple and invariable unit, the beginning of all form; the first and main element of attenuated organisms. It is the organic cell. The loftiest trees have bowed their heads, and confessed this strange secret of their structure.* The stubborn rock has not withheld the same tale of antediluvian lore. The highest animal and the lowest plant have narrated the self-imprinted story of their birth. Flowers have whispered it - the rustling leaves have breathed it. The butterfly has borne it on the dust of its wings, the fish upon its scales. It is written in the blood that circulates in our veins - it is imprinted on the muscle which gives motion, and the bones which afford support to our frame. All nature testifies to it. One secret that is the key of all shapely beauty or deformed ugliness - a hidden unity amidst all variety - a common type for every form.

One word which all creation perpetually utters; a witness to the one source whence all derives.

The waters teem with dissimilar forms of life. The air is darkened with inhabitants, not one of which has its exact counterpart. The mind actually shrinks from the contemplation of endless dissimilarity, and apparently inharmonious difference. What a chasm gapes between the shape and function of the stately old chestnut-tree of Etna, whom time has not subdued and age has not withered, and the ephemeral fungus that springs up to-day, flowers to-morrow, and dies ere another sun has visited it! A wider interval appears between the noble form of man himself and the green mould that clothes his tomb. But the microscope resolves this complexity, and bridges easily this chasm. It resolves them alive into simplest elements, and finds beneath all the same type of creation. It shows always, at the foundation, that common origin in cell-growth which binds all created things in one sublime connection; and proclaims a common law of growth, and a pervading fiat of creative power as vice-regent over organic nature.

It was our own distinguished countryman, Robert Brown, who initiated the observations whose fruitful results have led to the perception of this universal law. But not until the researches of Schleiden, in 1837, was any useful generalization obtained. The efforts of naturalists had, before that time, been chiefly directed towards the perception of differences and the creation of species. But Schleiden saw that the philosophy of nature was darkened by our ignorance of the laws of natural development; and bravely devoting himself to the patient study of growth, and the laws which control it, he travelled through a tangled forest of prickly and entwined facts, till at last he saw the light, and could proclaim it. He watched the secret processes of plants, traced them in their reproduction and their birth, analyzed their structures, and observed the process of their functional activities.

At the end of a long course of labor, he was able to tell the world that, as the minor organisms, which are the lowliest members of the vegetable kingdom, are each in themselves an individual cell, having life and activity, nutrition and reproduction, so the highest plants are only congeries of such individuals, heaped one upon another, moulded into a thousand shapes, and adapted to different purposes. It was then that he enunciated the principle that the life-story of a plant is to be studied through the vital history of its composing cell-elements; and, proclaiming the microscopic vegetable cell as the unit of vegetable creation, exalted it to the place of honor among the objects of microscopic research. It was no small thing that this key to the cabinet of vegetable physiology should be so discovered, and placed in our hands; but his researches led to yet another result - for Schwann proceeded to apply to the animal world the same method of inquiry which Schleiden had inaugurated among plants; and, at the close of two years, he made known, in his turn, the sublime truth that the law of formation and reproduction which prevails in the vegetable rules also over the animal creation. He showed that the scheme is the same, and the cells still the primordial element of being.