and may be again stimulated; and when each petal, with its annexed filament, has fallen to the ground, the latter, on being touched, shows as much sensibility as ever.' These singular effects are produced by the power of contractility or irritability, the nature of which will fall under consideration hereafter. It is possessed equally by animals and vegetables, and is essentially organic and vital. This power, we shall see, needs not the intervention of volition; it is constantly exerted in the animal without consciousness, and therefore necessarily without volition. Its existence in vegetables does not, consequently, demonstrate that they are possessed of consciousness. 4. Nutrition.--A great difference exists between plants and animals in this respect. The plant, being fixed to the soil, cannot search after food. It must be passive; and obtain its supplies from the materials around, and in contact with it; and the absorbing vessels of nutrition must necessarily open on its exterior. In the animal, on the other hand, the aliment is scarcely ever found in a state fit for absorption; it is crude, and in general-Ehrenberg thinks always-requires to be received into a central organ or stomach, for the purpose of undergoing changes, by a process termed digestion, which adapts it for the nutrition of the individual. The absorbing vessels of nutrition arise, in this case, from the internal or lining membrane of the alimentary tube. The analogy that exists between these two kinds of absorption. is great, and had not escaped the attention of the ancients:-Quemadmodum terra arboribus, ita animalibus ventriculus sicut humus" was an aphoristic expression of universal reception. With similar feelings, Boerhaave asserts, that animals have their roots of nutrition in their intestines; and Dr. Alston has fancifully termed a plant an inverted animal. After all, however, the most essential difference consists in the steps that are preliminary to the reception of food. These, in the animal, are voluntary-requiring prehension; often locomotion; and always consciousness. 5. Reproduction.-In this function we find a striking analogy between animals and vegetables; but differences exist, which must be referred to the same cause that produced many of the distinctions already pointed out, the possession, by the animal, of sensibility and locomotility. For example, every part of the generative act, as before remarked, is, in the vegetable, without the perception or volition of the being-the union of the sexes, fecundation, and the birth of the new individual are alike automatic. In the animal, on the other hand, the approximation of the sexes is always voluntary, and effected consciously the birth of the new individual being not only perceived, but somewhat aided by volition. Fecundation alone is involuntary and irresistible. Again, in the vegetable the sexual organs do not exist at an early period; and are not developed until reproduction is practicable. They Sir J. E. Smith's Introduction to Botany, p. 325. 2 Edinb. New Philosophical Journal, for Sept., 1831; and Jan., 1838, p. 232. are capable of acting for once only, and perish after fecundation; and if the plant be vivacious, they fall off after each reproduction, and are annually renewed. In the animal, on the contrary, they exist from the earliest period of foetal development, survive repeated fecundations, and continue during the life of the individual. Lastly, the possession of sensibility and locomotility leads to other characteristics of animated beings. These functions are incapable of constant, unremitting exertion. Sleep, therefore, becomes necessary. The animal is also capable of expression, or of language, in a degree proportionate to the extent of his sensibility, and of his power over the beings that surround him. But these differences in function are not so discriminate as they may appear at first. There are many animals, that are as irresistibly attached to the soil as the vegetables themselves. Like the latter, they must, of necessity, be compelled to absorb their food in the state in which it is presented to them. Sensibility and locomotility appear, in the zoophyte, to be no more necessary than in the vegetable. No nervous, no muscular system is required; and, accordingly, none can be traced in them; whilst many of those spontaneous motions of the vegetable, to which allusion has been made, have been considered by some to indicate the first rudiments of sensibility and locomotility; and Linnæus' has regarded the closure of the flowers towards night as the sleep, and the movements of vegetables, for the approximation of the sexual organs, as the marriage, of plants. II. GENERAL PHYSIOLOGY OF MAN. The observations made on the differences between animals and vegetables have anticipated many topics, that would require consideration under this head. The general properties, which man possesses along with other animals, have been referred to in a cursory manner. They will now demand a more special investigation. 1. MATERIAL COMPOSITION OF MAN. The detailed study of human organization is the province of the anatomist-of its intimate composition, that of the chemist. In explaining the functions executed by the various organs, the physiologist will frequently have occasion to trench upon both. The bones, in the aggregate, form the skeleton. The base of the skeleton is a series of vertebrae, with the skull as a capital-itself regarded as a vertebra. This base is situate on the median line through the whole trunk, and contains a cavity, in which are lodged the brain. and spinal marrow. On each side of this, other bones, which by some have been called appendices, are arranged in pairs. Upon the skeleton are placed muscles, for moving the different parts of the body; and for changing its situation with regard to the soil. The body is divided into trunk and limbs. The trunk, which is the principal portion, is composed of three splanchnic cavities, the abdomen, thorax, and head, Amonit. Academ., tom. iv. See, on all this subject, Robin and Verdeil, Traité de Chimie Anatomique et Physiologique, &c. Paris 1853. situate one above the other. They contain the most important organs of the body-those that effect the functions of sensibility, digestion, respiration, circulation, &c. The head comprises the face, in which are the organs of four of the senses-sight, hearing, smell, and taste,— and the cranium, which lodges the brain-the organ of the mental manifestations, and the most elevated part of the nervous system. The thorax or chest contains the lungs-organs of respiration-and the heart, the central organ of the circulation. The abdomen contains the principal organs of digestion, and (if we include in it the pelvis), those of the urinary secretion and of generation. Of the limbs, the upper, suspended on each side of the thorax, are instruments of prehension; and are terminated by the hand, the great organ of touch. The lower are beneath the trunk; and are agents for supporting the body, and for locomotion. Vessels, emanating from the heart, are distributed to every part-conveying to them the blood necessary for their life and nutrition: these are the arteries. Other vessels communicate with them, and convey the blood back to the heart-the veins; whilst a thirdset arise in the tissues, and convey into the circulation, by a particular channel, a fluid called lymph—whence they derive the name lymphatics. Nerves, communicating with the great central masses of the nervous system, are distributed to every part; and lastly, a membrane or layer, possessed of acute sensibility-the skin-serves as an outer envelope to the whole body. It was before observed, that two kinds of elements enter into the composition of the body-the chemical or inorganic; and the organic, which are compound, and formed only under the force of life. The chief CHEMICAL or INORGANIC ELEMENTS met with are: oxygen, hydrogen, carbon, nitrogen, phosphorus, calcium; and, in smaller quantity, sulphur, iron, manganese, calcium, silicium, aluminium, chlorine; also, sodium, magnesium, &c. &c. 1. Oxygen. This is widely distributed in the solids and fluids; and a constant supply of it from the atmosphere is indispensable to animal life. It is almost always found combined with other bodies; often in the form of carbonic acid,-that is, united with carbon. In a separate state it is met with in the air-bag of fishes, in which it is found varying in quantity, according to the species, and the depth at which the fish has been caught. 2. Hydrogen. This gas occurs universally in the animal kingdom. It is a constituent of all the fluids, and of many of the solids; and is generally in a state of combination with carbon. In the human intestines it has been found pure, as well as combined with carbon and sulphur. 3. Carbon. This substance is met with under various forms, in both fluids and solids. It is most frequently found under that of carbonic acid. Carbonic acid has been detected in an uncombined state in urine by Prout; and in the blood by Vogel.' It exists in the intestines of animals; but is chiefly met with in animal bodies, in combination with the alkalies or earths; and is emitted by all animals in the act of respiration. Annals of Philosophy, vii. 56. 4. Nitrogen. This gas is likewise widely distributed as a component of animal substances, and especially of the tissues. It occurs in an uncombined state, in the swimming-bladder of certain fishes. 5. Phosphorus is an essential constituent of neurine; and is found united with oxygen, in the state of phosphoric acid, in many of the solids and fluids. It is this acid that is combined with the earthy matter of bones; and with potassa, soda, ammonia, and magnesia, in other parts. It is supposed to give rise to the luminousness of certain animals-as of the fire-fly, Pyrosoma Atlanticum, &c.-but nothing precise is known on this subject. 6. Calcium. This metal is found in the animal economy in the state of oxide-lime; and it is generally united with phosphoric or carbonic acid. It is the earth, of which the hard parts of animals are constituted. 7. Sulphur is not met with extensively in animal solids or fluids; nor is it often found free, but usually in combination with oxygen united to soda, potassa, or lime. It seems to be an invariable concomitant of albumen; and is found in the intestines, in the form of sulphuretted hydrogen; and as an emanation from fetid ulcers. 8. Iron. This metal has been detected in the colouring matter of the blood; in bile, and in milk. In the first of these fluids it was, for a long time, considered to be in the state of phosphate or sub-phosphate. Berzelius' showed, that this was not the case; that the ashes of the colouring matter always yielded oxide of iron in the proportion of 1-200th of the original mass. That distinguished chemist was, however, unable to detect the condition in which the metal exists in the blood; and could not discover its presence by any of the liquid tests. Subsequently, Engelhart showed, that the fibrin and albumen of the blood, when carefully separated from colouring particles, do not contain a trace of iron; whilst he could procure it from the red corpuscles by incineration. He also succeeded in proving its existence in the red corpuscles by liquid tests; and his experiments were repeated, with the same results, by Rose of Berlin. In milk, iron seems to be in the state of phosphate. 9. Manganesium has been found in the state of oxide, along with iron, in the ashes of the hair; in bones, in gall-stones, and in the blood. 10. Copper and lead.-It was conceived by M. Devergie, that copper and lead may exist naturally in the tissues; but MM. Flandin and Danger, and a commission of the Académie Royale de Médecine of Paris, were unable to confirm the existence of copper; and the results. of the investigations of Professor F. de Cattanei di Momo, of Pavia, seem to prove the non-existence of lead also. M. Barse, however, in a paper read before the Royal Academy of Sciences of Paris, in August, 1843, states, that he found both metals in the bodies of two Medico-Chirurgical Transact., vol. iii. 2 Turner's Chemistry, fifth ed., p. 963. London, 1834. 3 Bullet. de l'Académ. Royale de Médecine, 19 Févr., 1839. Annali Universali di Medicina, Aprile, 1840; cited in British and Foreign Medical Review, Jan., 1841, p. 226. persons, to whom they could not have been given for poisons. The researches of Signor Cattanei di Momo appeared to prove that these metals do not exist in the bodies of new-born children or infants; and M. J. Rossignon has offered a solution as to the probable source of the copper, which he found not only in the blood and muscles of the dog, but in many articles of vegetable and animal food; in gelatin from bones, for example, in sorrel, chocolate, bread, coffee, succory, madder, and sugar. The ashes obtained from starch sugar yielded 4 per cent. of copper; those of gelatin, 0·03 per cent.; and those of bread, 0·005 to 0-008 per cent. It is now generally considered to be present in the human liver, and M. E. Millon' asserts, that human blood invariably contains lead, copper, silica, and manganese. 11. Silicon.-Silica is found in the hair, bones, blood, urine, and in urinary calculi. 12. Chlorine.-In combination with hydrogen, and forming chlorohydric acid, chlorine is met with in most of the animal fluids. It is generally united with soda. Free chlorohydric acid has also been found by Dr. Prout in the stomach of the rabbit, hare, horse, calf, and dog; and he has discovered the same acid in the sour matter ejected from the stomachs of those labouring under indigestion. Mr. Children, and Messrs. Tiedemann and Gmelin, made similar observations; and Professor Emmet and the author found it in considerable quantity in the healthy gastric secretions of man. 13. Fluorine. This simple substance has been found combined with calcium-fluoride of calcium-in the enamel of the teeth, bones, and urine. 14. Sodium.-Oxide of sodium, soda, forms part of all the fluids. It has never been discovered in a free state; but it is united (without an acid), to albumen. Most frequently, it is combined with chlorine, and phosphoric acid; less frequently, with lactic, carbonic, and sulphuric acids. Chloride of sodium is contained in most of the animal secretions; and from its decomposition may result the chlorohydric acid of the gastric juice, and a part of the soda of the bile and other fluids. 15. Potassium.-The oxide, potassa, is found in many animal fluids, but always united with acids-sulphuric, chlorohydric, phosphoric, &c. It is much more common in the vegetable kingdom; and hence one of its names-vegetable alkali. 16. Magnesium.-The oxide, magnesia, exists sparingly in bones, and in some other parts; but always in combination with phosphoric acid, and appears to be always associated with calcium. 17. Aluminium.-Alumina is said by Morichini to exist in the enamel of the teeth. Foureroy and Vauquelin found it in the bones; and Lond. Med. Gaz., Dec. 1, 1843, from Gazette Médicale de Paris, and Mr. Paget, Rep. on Anatomy and Physiology, 1843-4, in Brit. and For. Med. Rev., Jan., 1845, p. 249. 2 Kirkes and Paget, Manual of Physiology, 2d Amer. edit., p. 29, Philad., 1853. 3 Comptes Rendus, Paris, 1848. Philosoph. Transact. for 1824, p. 45. Recherches Expérimentales, &c., sur la Digestion, trad. par A. G. L. Jourdan. Art. 4, p. 94, Paris, 1827. See under the head of " Digestion," and the author's Human Health, p. 191, Philadelphia, 1844. |