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flourish entirely covered with water, or with their roots alone shooting into a moist soil.
Animals of various kinds are aërial : perhaps the term is not used with strict correctness. It will, at least, apply with more correctness to plants. All the most succulent plants of hot climates are of this description: such are several of the palms and of the canes; and the greater number of plants that embellish the arid Karro fields of the Cape of Good Hope. Succulent as they are, these will only grow in soils or sands so sere and adust that no moisture can be extracted from them, and are even destroyed by a full supply of wet or by a rainy season. The Solandra grandiflora, a Jamaica shrub, was long propagated in our own stoves by cuttings, which, though freely watered, could never be made to produce any signs of fructification, notwithstanding that the cuttings grew several feet in length every season. By accident å pot with young cuttings was mislaid and forgotten in the Kew garden, and had no water given it; it was hereby reduced to its healthy aridity, and every extremity produced a flower.f
And hence it is an opinion common to many of the ablest physiologists of the present day, that these derive the whole of their nutriment from the surrounding atmosphere; and that the only advantage which they acquire from thrusting their roots into such strata is that of obtaining an erect position. There are some quadrupeds that appear to derive nutriment in the same manner. Thus the bradypus tridactylus, or sloth, never drinks, imbibes by its cutaneous absorbents, and trembles at the feeling of rain; and, in common with the bird tribes, has only one ultimate or excrementary duct; while the olive cavyť avoids water of every kind almost as pertinaciously as does also the ostrich, which is in consequence said by the Arabs never to drink. And yet these are animals almost as succulent as any we are acquainted with.
But, however true this may be with regard to animals, we have manifest proofs that vegetables of certain tribes and descriptions are altogether supported by the atmosphere that surrounds them; for, important as is the organ of a root to plants in general, there are several which have no root whatever, and can derive nutriment in no other way. The water-caltropp is an instance directly in point. The seed of this plant has no rostel, and consequently can never, in the first instance, become rooted. From the horned nut or pericarp of the seed, as it lies in water, which is its natural element, shoots forth a long plumule perpendicularly towards the surface of the stream ; during the ascent of which a variety of capillary branched leaves shoot forth from the sides of the plumule, some of which bend downward, and fix the whole plant to the bottom by penetrating into the soil below the stream; the leaves alone in this late stage of germination acting the part of a root, and giving maturity to the still unfinished plant. The cactus genus, in some of its very numerous species, offers us an example of similar evolution; and especially in the opuntia tribe, or that which embraces the prickly pears or Indian figs of our green-houses, of which the cochineal plant|| is one form. Of these, several grow by the mere introduction of one of their thick fleshy leaves into a soil of almost any kind that is sufficiently dry; they obtain an erect position, but never root, or shoot forth radicles: and hence almost the whole of their moisture must necessarily be derived from the surrounding atmosphere.
Perhaps one-half of the fuci have no root whatever: many of them, indeed, consist of vesicles or vesicular bulbs alone, sessile upon the matrix of some stone or shell that supports them, and propagate their kinds by offsets, without any other vegetable organs. The seeds of the fucus prolifer sometimes evolve nothing but a leaf; the plant being propagated also by leaf upon leaf, either forked or elliptic, without root.
The aphyteia hydnora is a curious instance in point. This plant is equally destitute of leaves, stem, and root; and consists alone of a sessile, coriaceous,
The only rain that waters this tract is that which falls for a few weeks in the winter : during the hot and fertile months there is no rain whatever.
Smith's Introduction to Botany, &c. p. 141. Cavia acuschy. This is the more extraordinary, because the C. cobaya, or guinea-pig, drinks freely, and the C. capybara, or river cavy, is fond of swimming and diving. $ Trapa natans
# Cactus coccinellifer.
and succulent flower, eaten as a luxury by the Hottentots, and parasitic to the roots of the euphorbia mauritanica ; flower propagating flower from generation to generation.
But perhaps the plant most decisive upon this subject is the aërial epidendrum,* first, if I mistake not, described by that excellent Portuguese phytologist Loureiro, and denominated aërial froin its very extraordinary properties. This is a native of Java and the East Indies beyond the Ganges; and, in the latter region, it is no uncommon thing for the inhabitants to pluck it up, on account of the elegance of its leaves, the beauty of its flower, and the exquisite odour it diffuses, and to suspend it by a silken cord from the ceilings of their rooms; where, from year to year, it continues to put forth new leaves, new blossoms, and new fragrance, excited alone to new life and action by the stimulus of the surrounding atmosphere.
That stimulus is oxygen; ammonia is a good stimulus, but oxygen possesses far superior powers, and hence without some portion of oxygen few plants can ever be made to gerininate. Hence, too, the use of cow-dung and other animal recrements, which consist of muriatic acid and ammonia : while in fat, oil, and other fuids, that contain little or no oxygen, and consist altogether, or nearly so, of hydrogen and carbon, seeds may be confined for ages without exhibiting any germination whatever. And hence, again, and the fact deserves to be extensively known, however torpid a seed may be, and destitute of all power to vegetate in any other substance, if steeped in a diluted solution of oxygenated muriatic acid, at a temperature of about 46° or 48° of Fahrenheit, provided it still possess its principle of vitality, it will germinate in a few hours. And if, after this, it be planted, as it ought to be, in its appropriate soil, it will grow with as much speed and vigour as if it had evinced no torpitude whatever.
I have said that few plants can be made to germinate when the oxygen is small in quantity, and the hydrogen abundant: and I have made the limitation, because aquatic plants, and such as grow in marshes, and other moist places, are remarkable, not only for parting with a large quantity of oxygen gas, but also for absorbing hydrogen gas freely; and are hence peculiarly calculated for purifying the regions in which they flourish, and in some sort for correcting the mischief that flows from the decomposition of the dead vegetable and animal materials that is perpetually taking place in such situations, and loading the atmosphere with febrile and other miasms:
But the instances of resemblance between animal and vegetable physiology are innumerable. Some plants, like a few of our birds, more of our insects, and almost all our forest beasts, appear to sleep through the day, and to awake and become active at night: while the greater number, like the greater number of animals, resign themselves to sleep at sunset, and awake reinvigorated with the dawn. Like animals, they all feel the living power excited by small degrees of electricity, but destroyed by severe shocks; and like ani. mals, too, they differ in a very extraordinary degree in the duration of many of their species. Some tribes of boletus unsold themselves in a few hours, like the ephemera and hemerobius tribes (May-fly and Spring-fly), and as speedily decay. Several of the fungi live only a few days; others weeks or months. Annual plants, like the greater part of our insects, live three, four, or even eight months. Biennial plants, like the longer-lived insects, and most of our shell-fishes, continue alive sixteen, eighteen, or even twenty-four months. Many of the herbaceous plants continue only a few years, but more for a longer period, and imitate all the variety to be met with in the greater number of birds, quadrupeds, and fishes; while shrubs and trees are, for the most part, coequal with the age of man, and a few of them equal that allotted to him in the earliest periods of the world. Of these last, the Adansonia digitata, or calabash tree, is perhaps one of the most extraordinary, Indigenous to the land of the patriarchs, and still outrivalling the patriarchal age, this stupendous tree, compared with which our own giant oak, in bulk as well
Epidendrum flos aeris.
as in years, is but an infant, seems to require not less than a thousand years to give it full vigour and maturity. Extending its enormous arms over the dry and barren soil from which it shoots naturally, it affords shelter to whole nations of barbarians, and in its pleasant subacid fruit administers an ample supply to their hunger.
Let it not, however, be imagined that, by pointing out such frequent instances of resemblance between animal and vegetable life, I mean to degrade the rank of animal being from its proper level; for it will be one of the chief objects of our subsequent studies to develope and delineate its multiform and characteristic superiorities. I am only tracing at present the common principle of vitality to its first outlines: I am endeavouring to unfold to you, in its simplest and rudest operations, that grand, and wonderful, and comprehensive system, which, though under different modifications, unquestionably controlling both plants and animals, from the first moment it begins to act infuses energy into the lifeless clod, draws forth form and beauty, and individual being, from unshapen matter, and stamps with organization and propensities the common dust we tread upon. And if, in this its lowest scale of operation,-if, under the influence of these its simplest laws, and the mere powers (so far as we are able to trace them) of contractility and irritability, it be capable of producing effects thus striking, thus incomprehensible, what may we not expect when the outline is filled up and the system rendered complete? What may we not expect when we behold, superadded to the powers of contractility and irritability, those of sensation and voluntary motion? What, more especially, when to these are still farther added the ennobling faculties of a rational and intelligent soul,—the nice organs of articulation and speech,-the eloquence of language,-the means of interchanging ideas, and of imbodying, if I may so express myself, all the phenomena of the mind?
Such are the important subjects to which our subsequent studies are to be directed. In the mean time, from the remarks which have already been hazarded, we cannot, I think, but be struck with the two following sublime characters, which pre-eminently, indeed, distinguish all the works of nature : -a grand comprehensiveness of scheme, a simple but beautiful circle of action, by which every system is made to contribute to the well-being of every system, every part to the harmony and happiness of the whole; and a nice, and delicate, and ever-rising gradation from shapeless matter to form, from form to feeling, from feeling to intellect, from the clod to the crystal, from the crystal to the plant, from the plant to the animal, from brutal life to man. Here, placed on the summit of this stupendous pyramid, lord of all around him, the only being through the whole range of ihe visible creation endowed with a power of contemplating and appreciating the magnificent scenery by which he is encompassed, and of adoring its Almighty Architect--at once the head, the heart, and the tongue of the whole-well, indeed, may he exult and rejoice! But let him rejoice with modesty. For, in the midst of this proud exaltation, it is possible that he forms but one of the lowest links in " the golden everlasting chain” of intelligence; that he stands on the mere threshold of the world of perception; and that there exists at least as wide a disproportion between the sublimest characters that ever were born of women, our Bacons, Newtons, and Lockes, our Aristotles, Des Cartes, and Eulers, and the humblest ranks of a loftier world, as there is between these highly-gifted mortals and the most unknowing of the animal creation. Yet MIND, thanks to its benificent Bestower! is itself immortal, and knowledge is eternally progressive ; and hence man, too, if he improve the talents in. trusted to him, as it is his duty to do, may yet hope, unblamed, to ascend hereafter as high above the present sphere of these celestial intelligences, as they are at present placed above the sphere of man. But these are speculations in some degree too sublime for us : the moment we launch into them, that moment we become lost, and find it necessary to return with suitable modesty to our proper province,-an examination of the world around us ; 'where, with all the aids of which we can avail ourselves, we shall still find difficulties enough to try the wisdom of the wisest, and the patience of the most persevering.
ON THE PRINCIPLE OF LIFE, IRRITABILITY, AND MUSCULAR POWER.
We have distinguished organic from inorganic matter; and have characterized the former, among other differences, by its being actuated in every separate form by an internal principle, and possessed of parts mutually dependent and contributory to each other's functions. What then is this internal principle,-this wonderful and ever active power, which, in some sort or other, equally pervades animals and vegetables—which extends from man to brutes, from brutes to zoophytes, from zoophytes to fucuses and conservas, the lowest tribes of the vegetable kingdom, whose general laws and phenomena constituted the subject of our last study,--this fleeting and evanescent energy, which, unseen, by the eye, untracked by the understanding, is only known, like its great Author, by its effects; but which, like him too, wherever it winds its career, is perpetually diffusing around it life and health, and harmony and happiness?
I do not here enter into the consideration of a thinking or intelligent principle, or even a principle of sensation, both which are altogether of distinct natures from the present, and to which I shall entreat your attention here. after; but confine myself entirely to that inferior but energetic power upon which the identity and individuality of the being depend, and upon a failure of which the individual frame ceases, the organs lose their relative connexion, the laws of chemistry, which have hitherto been controlled by its superior authority, assume their action, and the whole system becomes decomposed and resolved into its primary elements.
The subject is, indeed, recondite, but it is deeply interesting : it has occupied the attention of the wisest and the best of mankind in all ages; and though, after the fruitless efforts with which such characters have hitherto pursued it, I have not the vanity to conceive that I shall be able to throw upon it any thing like perfect daylight, you will not, I presume, be displeased with my submitting to you a brief outline of some few of the speculations to which it has given birth, together with the conjectures it has excited in my own mind.
of the innumerable theories that have been started upon this subject, the three following are those which are chiefly entitled to our attention. Life is the result of a general harmony or consent of action between the different organs of which the vital frame consists.-Life is a principle inherent in the blood.-Life is a gas, or aura, communicated to the system from without. Each of these theories has to boast of a very high degree of antiquity; and each, after having had its day, and spent itself, has successively yielded to its rivals; and in its turn has reappeared, under a different modification, in some subsequent age, and run through a new stage of popularity.
For the system OF HARMONY we are indebted to the inventive genius of Aristoxenus, a celebrated physician of Greece, who was at first a pupil of Lamptus of Erythræa, afterward of Xenophylus the Pythagorean, and lastly of Aristotle. He was most excellently skilled in music, and is supposed to have given the name of HARMONY to his system from his attachment to this science. It is an ingenious and elegant dogma, and was at one time highly fashionable at Rome as well as at Athens; and is thus alluded to and explained by Lactantius : “As in musical instruments, an accord and assent of sounds, which musicians term HARMONY, is produced by the due tone of the strings; so in bodies, the faculty of perception proceeds from a connexion and vigour of the members and organs of the frame."*
To this theory there are two objections, either of which is fatal to it. The first is, that admitting the absolute necessity of the health or perfection of every separate part to the health or perfection of the whole, we are still as much in the dark as ever in respect to the principle by which this harmonious machine has been developed, and is kept in perpetual play. The second objection, by which, indeed, it was vigorously attacked by the Epicureans, and at length completely driven from the field, is derived from observing that the health or well-being of the general system does not depend upon that of its collective organs; and that some parts are of far more consequence to it than others. Thus the mind, observes Lucretius, in his able refutation of this hypothesis, may be diseased, while the body remains unaffected; or the body, on the contrary, may lose some of its own organs, while the mind, or even the general health of the body itself, continues perfect.
* V. 140.
The abbé Polignac, who, consistently with the Cartesian system, makes a very proper distinction between the principle of the mind or soul, and that of the lise, enters readily into the hypothesis of Aristoxenus in regard to the latter power, though he thinks it inapplicable to the former: and Leibnitz appears to have availed himself of it as a ineans of accounting for the union between the soul and body in his celebrated system, which he seems to have named, from the theory before us, the system of PRE-ESTABLISHED HARMONY. By a writer of the present day, however, M. Lusac, the doctrine of Aristoxenus seems to have been resuscitated in its fullest scope, and even to have been carried to a much wider latitude than its inventor had ever intended: for the theory of M. Lusac affects to regard, not only the frame of man and other animals, but the vast frame of the universe, as a sort of musical organ or instrument; the concordant and accumulated action of whose different parts or agents he denominates, like Aristoxenus, harmony. “Concerts of music,” says he, “afford a clear example: you perceive harmony in music when different lones, obtained by the touch of various instruments, excite one general sound, a compound of the whole.” This observation he applies to the grand operations of nature, the irregularities of which, resulting from inundations, earthquakes, volcanoes, tempests, and similar evils, this philosopher considers as the dissonances occasionally introduced into music to heighten the harmony of the entire system. With respect to the harmony of the human frame, individually contemplated, or the concordant action of the different parts of the body, he observes, “It may be said, that of this principle I have merely a confused notion; and I admit it, if the assertion imply that I have neither a perfect nor a distinct, nor an entire comprehension of what produces this harmony-in what it consists, or how it acts. I know not what produces the harmony of various instruments heard simultaneously; but I can accurately distinguish the sounds which are occasioned when musicians are tuning, from those which are produced when, being completely in tune, and every one uniting in the piece, the separate parts are executed with precision. When I hear an harmonious sound, whatever be its nature, I can distinguish the harmony, though incapable of investigating its cause.
I shall only observe, farther, that in the doctrine of Mr. (now Sir Humphry) Davy, which holds life itself as a perpetual series of corpuscular changes, and the substrate, or living body, as the being in which these changes take place, we cannot but observe a leaning towards the same system; and we shall have occasion, in a subsequent lecture, to notice one or two others of equally modern date that touch closely upon it in a few points.
Let us pass on, then, to a consideration of the second hypothesis I have noticed, and which consists in regarding the blood ITSELF AS THE PRINCIPLE OF LIFE. This opinion lays claim to a still higher antiquity than the preceding; and, in a general view of the question, is far better founded. It has the fullest support of the Mosaic writings, which expressly appeal to the doc, trine, that “ the life of all flesh is the blood thereof," I as a basis for the culi
| Series ul. Lecture v.
* Du Droit Naturel, Civil, et Politique, tom. I. 154. 1 Levit xvii. 14.