1901. In animals with many feet, as the Myriopoda, walking is performed by so uniform a motion, that the body may be said to glide along the surface.

1902. In animals with four feet, "cach step is executed by two legs only; one belonging to the fore pair, and the other to the hind pair; but sometimes they are those of the same side, and sometimes those of opposite sides." (Cuvier's Comparative Anatomy, lect. vii, a, 1.) The latter is that kind of motion in horses, which grooms term a pace. The right fore-leg is advanced so as to sustain the body, which is thrown upon it by the left hind-foot, and at the same time, the latter bends in order to its being moved forward. While they are off the ground, the right hind-foot begins to extend itself, and the moment they touch the ground, the left fore-foot moves forward to support the impulse of the right foot, which likewise moves forward. The body is thus supported alternately by two legs placed in a diagonal manner. When the right fore-foot moves, in order to sustain the body, pushed forward by the right hind-foot, the motion is then called an amble. The body, being alternately supported by two legs on the same side, is obliged to balance itself to the right and left, in order to avoid falling; and it is this balancing movement which renders the gait so soft and agreeable to women and persons in a weak state of body. (Cuvier's Comp. Anat., lect. vii.)

1903. The serpentine motion consists in bringing up the tail towards the head by bending the body into one or more curves, then resting upon the tail, and extending the body, thus moving forward, at each step, nearly the whole length of the body, or one or more of the curves into which it was formed. Among the Mollusca, and many of the annulose animals, the same kind of motion is performed by alternate contractions and expansions, laterally and longitudinally of the whole body, or of those parts which are appropriated to progressive motion.

1904. A mode of moving analagous to walking, is performed by animals who have suckers, and is exemplified in the leech, which at every step advances nearly the whole length of its body.

1905. In the action of leaping, the whole body rises from the ground, and for a short period is suspended in the air. It is produced by the sudden extension of the limbs, after they have undergone an unusual degree of flexion. The extent of the leap depends on the form and size of the body, and the length and strength of the limbs. The Myriopoda are not observed to leap. Many of the spiders and insects leap with ease forwards, backwards, and laterally. In those which are remarkable for this faculty, the thighs of the hind-legs are in general of uncommon size and strength. Among reptiles the leaping frog is well known, in opposition to the crawling toad. Among quadrupeds, those are observed to leap best, which have the hind legs longer and thicker than the fore-legs, as the kangaroo and the hare. These walk with difficulty, but leap

with ease.

1906. Serpents are said to leap, by folding their bodies into several undulations, which they unbend all at once, according to the velocity they wish to give to their motion. The jumping maggot, found in cheese, erects itself upon its anus, then forms its body into a circle, bringing its head to the tail; and, having contracted every part as much as possible, unbends with a sudden jerk, and darts forward to a surprising distance. Many crabs and Podùræ bend their tail, or hairs which supply its place, under their belly, and then, suddenly unbending, give to the body a considerable degree of progressive motion.

1907. Flying. Flying is the continued suspension and progress of the whole body in the air, by the action of the wings. In leaping, the body is equally suspended in the air, but the suspension is only momentary; in flying, on the contrary, the body remains in the air, and acquires a progressive motion by repeated strokes of the wings on the surrounding fluid. The centre of gravity is always below the insertion of the wings in the bodies of flying animals to prevent them from falling on their backs, but near that point on which the body is, during flight, as it were suspended. The action of flying is performed by animals belonging to different classes. Among the Mammàlia, bats display this faculty, by means of wings, formed of a thin membrane extending between the toes, which are long and spreading, between the fore and hind legs, and between the hind legs and the tail. In birds, the wings, which occupy the place of the anterior extremities in the Mammàlia, and are the organs of flight, consist of feathers, which are stronger than those on the body, and of greater length. Among reptiles, the flying lizard may be mentioned, whose membranaceous wings, projecting from each side of the body, without being connected with the legs, enable it to fly from one tree to another in search of food. A few fishes are likewise capable of sustaining themselves for a short time by means of their fins; these are termed flying fish. Spiders are able to move in the air by means of their threads.

1908. Swimming is the same kind of action in water, as flying is in air. The organs which are employed for this purpose resemble the oars of a boat in their mode of action, and in general possess a considerable extent of surface and freedom of motion. Swimming, however, is not confined to those animals which are furnished with oars or swimmers. Many animals move with ease in the water by means of repeated undulations of the body, as serpents, eels, and leeches; or by varying the form of the body by alternate contractile and expansive movements, as the Medùsæ.

1909. In these different displays of voluntary motion, the muscles are only able to continue in exercise for a limited period, during which the irritability diminishes, and the further exertion of their powers becomes painful. When thus fatigued, animals endeavour to place themselves in a condition for resting, and fall into that state of temporary lethargy, denominated sleep.

1910. The positions assumed by animals during sleep are extremely various. In the horse, they even differ according to circumstances. In the field he lies down, in the

stable he stands.

Dogs and cats form their bodies into a circle, while birds place their

heads under their wings.

1911. The ordinary mode of sleep is likewise exceedingly various in different animals, and in the same animal is greatly influenced by habit. It in general depends on circumstances connected with food. It is probable, that all animals, however low in the scale, have their stated intervals of repose, although we are as yet unacquainted either with the position which many of them assume, or the periods during which they repose.

1912. The nervous system, by containing the organs of sensation and volition, is that which distinguishes animal from vegetable beings. It consists, in the vertebrated animals, of the brain, the spinal marrow, and the nerves.

1913. The brain, exclusive of its integuments, appears in the form of a soft, compres sible, slightly viscous mass. The spinal marrow originates with the brain, and consists of four cords united in one body. The nerves, also, originate in the brain or spinal marrow. Some of them appear to have a simple origin; but, in general, several filaments, from different parts of the brain or spinal marrow, unite to form the trunk of a nerve. This trunk again subdivides in various ways; but the ramifications do not always exhibit a proportional decrease of size. It frequently happens that the branches of the same nerve, or of different ones, unite and separate repeatedly within a small space, forming a kind of network, to which the name plexus has been applied. Sometimes filaments pass from one nerve to another; and, at the junction, there is usually an enlargement of medullary matter termed a ganglion. Numerous filaments, from different nerves, often unite to form a ganglion, from which proceed trunks frequently of greater magnitude than the filaments which entered. Thus nerves, very different in their origin, form communications with one another; so that the whole nervous system may be considered as a kind of network, between the different parts of which an intimate connection subsists. In consequence of this arrangement, it is often matter of very great difficulty to ascertain the origin of those filaments, which unite to constitute the trunk of a nerve. In some instances, they appear to arise from the surface of the brain or spinal marrow; in other cases, from the more central parts.

1914. The brain, in the animals without vertebra, is destitute of the protecting bony covering, which forms the head and back bone in the vertebral animals. The brain itself is much more simple in its structure. Independently of very remarkable differences in the structure of the nervous system in the different genera of invertebral animals, there may still be perceived two models, according to which, the organs belonging to it are arranged. In the first, the brain is situated upon the œsophagus, and presents different forms according to the species, appearing more like a ganglion than like the brain of the vertebral animals. It sends off several nerves to the mouth, eyes, and feelers. Two, one on each side, pass round the oesophagus, and, uniting below, form a ganglion in some cases larger than what is considered the true brain. From this ganglion, nerves are likewise sent off to different parts of the body. The animals in which this nervous system prevails belong to the great division termed Mollúsca. In the second, the brain is situated as in the Mollúsca, sending out nerves to the surrounding parts, and likewise one nerve on each side, which, by their union, form a ganglion, from which other nerves issue. This ganglion produces likewise a nervous cord, which proceeds towards the extremity of the body, forming throughout its length ganglia, from which small nerves proceed; this cord, at its commencement, is, in some cases, double for a short distance. It has been compared to the medulla oblongata, and spinal marrow of the vertebral animals. This kind of nervous system is peculiar to the annulose animals. There are usually ganglia on the nervous cord, corresponding with the number of rings of which the body consists.

1915. The functions of the brain and nervous system; the organs of perception, as of touch, of heat, of light, of hearing, of smell, and of taste; and also the faculties of the mind, we pass over as belonging chiefly to the anatomy and physiology of the human frame, and therefore less immediately connected with the animals used in agriculture. The reader will find these subjects ably treated by Dr. Fleming.

CHAP. III.

Animal Chemistry; or the Substances which enter into the Composition of the Bodies of Animals.

1916. The elementary principles of the animal kingdom have been ascertained with considerable precision; but the binary, ternary, or other compounds which they form, have not been investigated with so much success. As these various ingredients are

brought into union in the animal system by the agency of the vital principle, their state of combination may be expected to differ widely from the ordinary results of electric attraction. When such compounds of organisation are submitted to analysis, the influence of the vital principle having ceased, the products obtained may be regarded, in many cases, as modifications of the elements of the substance, occasioned by the processes employed, rather than the display of the number or nature of the ingredients, as they existed previously to the analytical operations. Hence the great caution requisite

in drawing conclusions regarding the composition of animal bodies.

1917. The elementary substances which are considered as entering into the parts of animals are, carbon, hydrogen, oxygen, azote, phosphorus, sulphur, fluoric acid, muriatic acid, iodine, potash, soda, ammonia, lime, magnesia, silica, iron, and manganese.

1918. Carbon exists in various states of combination in the fluids, as well as in the solids, of every animal; and has been detected in the form of charcoal in the lungs. When animal substances are exposed to a high temperature in closed vessels, the charcoal which is produced differs considerably from that which is obtained by the same means from vegetables. It is more glossy in appearance, and is incinerated with much greater difficulty.

1919. Hydrogen is universally distributed in the animal kingdom; it occurs as a constituent ingredient of all the fluids, and of many of the solids. It is invariably in a state of combination with charcoal; for, as far as we know, it has never been detected in an uncombined or separate state. It has been found in the human intestines, in the form of carburetted hydrogen.

1920. Oxygen is as widely distributed as the preceding, in the fluids and solids of all animals. A constant supply of it from the atmosphere is indispensably necessary to the continuation of animal life. It occurs, not only in combination with other bodies, but probably, likewise in a separate state, in the air-bag of fishes, in which it is found, varying in quantity, according to the species, and the depth at which the fishes have been caught. It is common, in union with charcoal, forming carbonic acid.

1921. Azotic gas is very widely distributed as a component part of animal substances. It occurs in almost all the fluids, and in those solid parts which have carbon as a base. The almost universal prevalence of this principle in animal substances constitutes one of the most certain marks by which they may be distinguished from vegetables. Azote likewise occurs, in an uncombined state, in the air-bag of some fishes.

1922. Phosphorus. This inflammable body exists, in union with oxygen, in the state of phosphoric acid, in many of the solids and fluids of animals. Its existence, however, in an uncombined state, has not been satisfactorily determined, although there appears a tendency to refer the luminousness of several animals to the slow combustion of this substance. Even phosphoric acid can scarcely be said to exist in a separate state, being found in combination with potash, soda, ammonia, lime, or magnesia.

1923. Sulphur, in combination, exists in considerable abundance in animal substances. It can scarcely be said to occur in a separate state in animals; at least, the experiments which may be quoted as encouraging such a supposition are by no means decisive. United with oxygen, in the form of sulphuric acid, it exists in combination with potash, soda, and lime.

1924. Fluoric acid has been detected in bones and urine, in a state of combination with lime.

1925. Muriatic acid exists in a great number of the animal fluids, in combination with an alkali, as in the ammonia and soda of urine.

1926. Iodine has been detected in sponge.

1927. Potash exists in combination with the sulphuric, muriatic, or phosphoric acids; but it is far from abundant in animal fluids.

1928. Soda is present in all the fluids in various states of combination, and is more abundant than the preceding It gives to many of the secretions the alkaline property of changing vegetable blues into green. It is found in union with the carbonic, phosphoric, sulphuric, and muriatic acids.

1929. Ammonia exists in its elements in all the fluids, and many of the solids, of animals, and is frequently produced during putrefaction. These elements are likewise found united in the system, and the alkali then appears in union with the various acids, as the phosphoric, muriatic, and lactic.

1930. Lime, of which the hard parts of animals, such as bones and shells, are principally composed, is of universal occurrence. It is always in a state of combination, and chiefly with the carbonic or phosphoric acids.

1931. Magnesia occurs sparingly. It has been detected in the bones, blood, and some other substances, but always in small quantity, and chiefly in union with phosphoric acid.

1932. Silica occurs more sparingly than the preceding. It is found in the hair, urine, and urinary

calculi.

1933. Iron has hitherto only been detected in the colouring matter of the blood, in bile, and in milk. Its peculiar state of combination in the blood has given rise to various conjectures; but a satisfactory solution of the question has not yet been obtained. In milk, it appears to be in the state of phosphate. 1934. Manganese, in oxide, has been observed, along with iron, in the ashes of hair.

1935. Such are the simple substances which have been detected by chemists in the solids and fluids of animals; but seldom in a free state, and often in such various proportions of combination to render it extremely difficult to determine their true condition.

1936. The compounds of organisation are gelatine, albumen, fibrin, mucus, urea, sugar, oils, and acids.

1937. Gelatine occurs in nearly a pure state in the air-bags of different kinds of fishes, as, for example, isinglass, which, if dissolved in hot water and allowed to cool, forms jelly. When a solution of tannin is dropped into a solution of gelatine, a union takes place, and an insoluble precipitate of a whitish colour falls to the bottom. It is on the union of the tannin of the oak bark with the gelatine of the hides, that the process of tanning leather depends. Gelatine exists in abundance in different parts of animals, as bones, muscles, skin, ligaments, membranes, and blood. It is obtained from these substances by boiling them in warm water; rentoving the impurities, by skimming, as they rise to the surface, or by subsequent straining and clarifying. It is then boiled to a proper consistence. It is the characteristic ingredient of the softest and most flexible parts of animals.

1938. Gelatine is extensively used in the arts, under the names of glue and size, on account of its adhesive quality, and to give the requisite stiffness to certain articles of manufacture. In domestic economy, it is likewise employed in the form of jelly, and in the formation of various kinds of soup. What is termed Portable Soup is merely jelly which has been dried, having been previously seasoned, according to the taste, with different spices.

1939. Albumen, the white of an egg, exists in great abundance, both in a coagulated and liquid state, in the different parts of animals. Hair, nails, and horn are composed

of it. It appears likewise as a constituent of bone and shell; and there are few of the fluid or soft parts of animals in which it does not exist in abundance. What has hitherto been termed the Resin of Bile is, according to Berzelius, analogous to albumen. 1940. Albumen is extensively used in the arts. When spread thin on any substance, it soon dries, and forms a coating of varnish. Its adhesive power is likewise considerable. When rubbed on leather, it increases its suppleness. But its chief use is in clarifying liquors. For this purpose, any substance abounding in albumen, as the white of eggs, or the serum of blood, is mixed with the liquid, and the whole heated to near the boiling point. The albumen coagulates, and falls to the bottom, carrying along with it the impurities which were suspended in the fluid, and which rendered it muddy. If the liquor contains alcohol, the application of heat is unnecessary.

1941. Fibrin exists in the blood, and was formerly called the fibrous part of the blood. It likewise exists in all muscles, forming the essential part, or basis, of these It exhibits many remarkable varieties, as it appears in the flesh of quadrupeds, birds, and fishes; but has not hitherto been turned to any particular use.

organs.

1942. Extractive exists in the muscles of animals, in the blood, and in the brain. It communicates the peculiar flavour of meat to soups. In the opinion of Fourcroy, the brown crust of roasted meat consists of it.

1943. The soft parts of animals are constituted of these four substances, which also enter into the composition of the hard parts and of the Huids. They are readily distinguishable from one another. Extractive alone is soluble in alcohol; gelatine is insoluble in cold, but soluble in hot, water; albumen is soluble in cold, and insoluble in hot, water; the fibrin is equally insoluble in hot and cold water. They are variously mixed or united; and as they consist of some elementary principles, chiefly carbon, hydrogen, oxygen, and azote, it is probable that they are in many cases changed, the one into the other, by the living principle; a transmutation which the chemist has succeeded in accomplishing, and which may soon be of advantage in the arts. The proportion of carbon appears to be least in gelatine and greatest in fibrin.

1944. Mucus occurs in a liquid state in the animal economy, as a protecting covering to different organs. It necessarily differs in its' qualities, according to the purposes it is destined to serve. In the nose, it defends the organ of smell from the drying influence of the air; in the bladder, it protects the interior from the contact of the acid of the urine; while it preserves the gall-bladder from the action of alkaline bile. It does not contain any suspended particles like the blood, but is homogeneous. (Dr. Young, Annals of Phil., vol. ii. p. 117.) When inspissated, it constitutes, in the opinion of some, the basis of the epidermis, horns, nails, and feathers. But the difficulty of obtaining it in a pure state, and the discordant characters assigned to it by different chemists, prevent us from reposing confidence in the accuracy of the analysis of those substances, of which it is considered as forming an essential ingredient.

1945. Urea is a substance obtained by evaporation and trituration from the urine of the Mammalia when in a state of health. In the human subject it is less abundant after a meal, and nearly disappears in the disease called diabetes, and in affections of the liver.

1946. Sugar exists in considerable abundance in milk, and in the urine of persons labouring under diabetes. In the latter fluid, it is to be considered as a morbid secretion of the kidneys, occupying the natural situation of the urea. In milk, however, it exists as a constituent principle, and may readily be obtained by the following process: evaporate fresh whey to the consistence of honey, dissolve it in water, clarify with the whites of eggs, and again evaporate to the consistence of syrup. On cooling, white cubical crystals will be obtained, but less sweet than vegetable sugar.

1947. Oils vary greatly as to colour, consistence, smell, and other characters. They possess, however, in common, the properties of the fixed oils, in being liquid, either naturally or when exposed to a gentle heat, insoluble in water and alcohol, leaving a greasy stain upon paper, and being highly combustible. They are distinguished as spermaceti, ambergris, fat, and common oils.

1948. Spermaceti constitutes the principal part of the brain of the whale, and is freed from the oil which accompanies it by draining and squeezing, and afterwards by the employment of an alkaline lie, which saponifies the remainder. It is then washed in water, cut into thin pieces with a wooden knife, and exposed to the air to dry. It is used in medicine and candlemaking.

1919. Ambergris is found in the intestines of the spermaceti whale, and in those only which are in a sickly state. It appears to be the excrement, altered by a long retention in the intestines, and therefore scarcely merits a place among the natural ingredients of the animal system. Upon being voided by the animal, it floats on the surface of the sea, and has been found in various quarters of the globe. It usually has the beaks of cuttle-fish adhering to it. It is employed in small quantities by druggists and perfumers, 1950 Fat consists of two substances, suet and oil. It is usually purified by separating the vessels and membranes which adhere to it, by repeatedly washing with cold water, and afterwards melting it, along with boiling water.

1961. Tallow is the fat of ruminating animals, and is hard and brittle; while the fat of the hog, called lard, is soft and semifluid. Its uses, as an article of food, in the making of candles, hard soap, and ointments, and to diminish friction, are well known.

1952 The properties of oils depend in a great degree on the mode of preparation, with the exception of the odour, which arises from the kind of animal from which the oil has been derived. Spermaceti oil is considered as the thinnest of the animal oils, and the fittest for burning in lamps. It is obtained from the spermaceti, by draining and pressure. Train oil is procured by melting the blubber, or external layer of fat, found underneath the skin of different kinds of whales and seals. From the process employed, it

contains, besides the oil, gelatine, albumen, and other animal matters, which render it thick, darkcoloured, and disposed to become rancid. Fish oil is sometimes extracted from the entire fish (as the sprat, pilchard, and herring, when they occur in too great quantities to be salted), by boiling in water, and skimming off the oil, as it appears on the surface. In general, however, the oil is obtained from the livers of fish, in which it is lodged in cells.

1953. The acids found in animals consist of various proportions of carbon, hydrogen, oxygen, and azote. Some of them are peculiar to the animal kingdom, and others exist in equal abundance in plants.

1954. The uric or lithic acid abounds in urine, and appears to be a production of the kidneys. The lactic acid is common in the animal fluids. The amniotic acid has been found in the uterus of a cow. The formic acid is procured by distilling ants. The benzoic, oxalic, acetic, and malic acids are common both to plants and animals, but seldom occur in the latter.

1955. These elements, by combining in different proportions, exhibit a great variety of separate substances. The earthy salts are likewise abundant; and when they occur in a separate state, they strengthen the albuminous framework, and form the skeleton, giving stability to the body, and acting as levers to the muscles. The alkaline salts occur in the greatest abundance in the secreted fluids.

1956. The fluids consist of those juices which are obtained from our food and drink, such as the chyle, and are termed crude of the blood, or prepared from the crude fluids, and destined to communicate to every part of the body the nourishment which it requires; and of those fluids which are separated from the blood, in the course of circulation, such as the bile, and termed secreted fluids. These are all contained in appropriate vessels, and are subject to motion and change.

1957. The solids are derived from the fluids, and are usually divided into the soft and hard. The soft solids consist chiefly of what is termed animal matter, of combinations of carbon, hydrogen, oxygen, and azote. They consist of fibres, which are usually grouped into faggots; of plates, which, crossing one another in various directions, give rise to cellular structure, or of a uniform pulpy mass.

1958. The fibrous texture may be observed in all the muscles, tendons, and ligaments, and in the bones of many animals, especially before birth. These fibres, however minutely divided, do not appear to be hollow, like those of the vegetable kingdom.

1959. The cellular texture is universally distributed in the form of membranes, which invest every organ, the bundles of fibres in every muscle, and, by forming tubes with the addition of the fibrous texture, constitute the containing vessels. The substance gives form to all the different parts, and is that particular portion which is first formed, and which constitutes the frame on and within which the other materials of the system are deposited. It readily expands by the increase of its contents; and, with equal ease, contracts, when the distending cause is removed.

1960. The pulpy texture is confined to the brain and nerves, the liver, kidneys, and other secreting organs of the system. Its composition appears to the eye homogenous, and its form is regulated by its cellular envelope.

1961. These soft solids alone are capable of possessing the faculty of sensation. By their aid, the nervous energy is exerted on the different parts of the body; and, through them, the impressions of external objects are received.

1962 The hard solids consist either of cartilage, which resembles, in its qualities, coagulated albumen; or of bone, formed by various combinations of earthy salts. They are destitute of sensation, and are chiefly employed in defending the system from injury, giving it the requisite stability, and assisting the muscles in the execution of their movements.

1963. The proportion between the solids and fluids is not only remarkably different in different species, but in the same species, in the various stages of growth.

CHAP. IV.

Animal Physiology; the Digestive, Circulating, and Reproductive Functions of Animals.

SECT. I. Of the Digestive System.

1964. The instinct of animals for food presides over the organs of the stomach. Hunger is felt when the stomach is empty; it is promoted by exercise, cold air applied to the skin, and cold, acid, or astringent fluids introduced into the stomach. Inactivity, warm covering, the attention diverted, and warm fluids, have a tendency to allay the sensation.

1965. Thirst is accompanied with a sensation of dryness in the mouth. This dryness may be occasioned by excessive expenditure of the fluids, in consequence of the dryness or saltness of the food which has been swallowed; or to their deficiency, from the state of the organs.

1966. Both hunger and thirst, besides being greatly influenced by habit, exhibit very remarkable peculiarities, according to the species and tribes of animals.

1967. Those which live on the spoils of the animal kingdom are said to be carnivorous, when they feed on flesh; piscivorous, when they subsist on fishes; and insectivorous, when they prey on insects. Again, those animals which are phytivorous, or subsist on the products of the vegetable kingdom, are either granivorous and feed on seeds; graminivorous, pasturing on grass; or herbivorous, browsing on twigs and shrubs.