76 



FIRST CLASS OF THE VERTEBRATED ANIMALS. 



The changes of all these bodies partake more or less of Iho same (general cbaracter. 

 A tree may be considered as a body composed of an infinite number of germs which 

 are successively developed. Besides the fruit produced each year, it pushes forth an 

 immense number of leaves, which estrcct their nutriment from the sap, expand, and 

 arrive at their full growth. Then having received all the nutriment which the arioloR 

 of their tissue can maintain, they dry up, become yellow or brown, the leaf ceases to 

 extract the sap, and dies of old age. The vessels of the petiole are broken by this 

 drying up and obstruction, and the loaf falls. This is observed generally in autumn 

 with the trees of our climates, and happens also in the ever-green trees, the only 

 difference being, that in these the new leaves are repaired as fast as the old ones 

 full, so that the tree is not at any one time completely destitute of verdure. 



The same thing happens with the feathers of Birds, and the hair of the Mam- 

 malia. The bulbous root of the hair is penetrated by a blood-vessel, and that portion 

 of nutriment and growth necessary to its development is thence communicated to the 

 shaft. "When the root dries, and the canal ceases to admit nutriment, the hair falls ; 

 the nutriment finds its way to other bulbs, the germs of hairs yet in embryo, con- 

 cealed beneath the epidermis ; and a new coat of hair succeeds to the former. Tlius 

 tlie hair is a kind of plant, which has its bulb or root, and its shaft or stalk, com- 

 posed of long sheathy tunics, one within another, like the tubes of a telescope. 



The castinvr of hair among the Mammalia arrives at different seasons, according to 

 the peculiar constitution of each animal in reference to Heat, and in general its de- 

 gree bears an immediate reference to the temperature of the district, whether arising 

 from the season of the year, the latitude of the place, or the degree of elevation, 

 '= In the warmer regions," says Dr Fleming, " it is requisite to have the temperature 

 of the body diminished, in the colder regions, the very opposite object is aimed at. 

 In the former case the hair or feathers are thinly spread out, while in the latter, they 

 form a close and continuous covering. In the Dogs of Guinea, and in the African and 

 Indian Sheep, the fur is so very thin that they may be almost denominated naked. In 

 the Siberian Dog and Iceland Sheep, on the other hand, the body is protected by a 

 thicker and longer covering. The clothing of animals, living in cold countries, is 

 not only different from that of the animals of warm regions in its quantity, but in its 

 arrano-ement. If we examine the covering of Swine of warm countries, we find it 

 consistino- of bristles or hair of the same form and texture ; while the same animals, 

 which live in colder districts, possess not only common bristles or strong hair, but a 

 fine frizzled wool next the skin, over which the long hairs project. Between the 

 Swine of the South of England and the Scottish Highlands, such differences may be 

 observed. Similar appearances present themselves among the Sheep of warm and 

 cold countries. The fleece of those of England consists entirely of wool, while the 

 Sheep of Shetland and Iceland possess a fleece, containing, besides the wool, a num- 

 ber of lonfi^ hairs, which give to it, when on the back of the animal, the appearance 

 of being very coarse. The living races of Rhinoceros and Elephant, inhabitants of 

 the warm regions, have scarcely any hair upon their bodies ; while those which for- 

 merly lived in the IS'orthern plains of Europe, the entire carcasses of which have 

 been preserved in the ice of Siberia, were covered with fur similar to the Iceland 

 Sheep, consisting of a thick covering of short-frizzled wool, protected by long coarse 

 hairs. These species, now extinct, possessed clothing, suiting them to the climate 

 where they hved, and where they became at la&t enveloped in ice. Had they been 

 transported by any accident from a warmer region, they would have exhibited in the 

 thinness of their covering, unequivocal marks of the climate in which they were reared. 

 Bv means of this arrangement, in reference to the quantity of clothing, individuals of 

 the same species can maintain life comfortably, in climates which differ considerably 

 in their average annual temperature. By the same arrangements, the individuals 

 residing in a particular district are able to provide against the varying temperature 

 of the seasons. The covering is diminished during winter, and increased in summer, 

 as may be witnessed in many of our domestic quadrupeds. Previous to winter, the 

 hair is increased in quality and length. This increase bears a constant ratio to the 

 temperature ; so that, when the temperature decreases with the elevation, we find 

 the Cattle and Horses, living on farms near the level of the sea, covered with a shorter 

 and thinner fur than those which inhabit districts of a higher level. Cattle and 

 Horses, housed during the winter, have shorter and thinner hair than those which 

 live constantly in the open air. The hair is hkewise shorter and thinner in a mild, 

 than during a severe winter." 



The approach of the hot seasons of each year, by occasioning the development of 

 new hair, transfers to them that nutrition which the former coat was in the habit of 

 receiving'. Hence, as the summer advances, the hair falls off, and the animal be- 

 comes sleek; and the warm covering of winter is exchanged for a lighter and more 

 commodious garb. The Sheep in our climates casts its fleece before the end of June, 

 and the Mole about the end of May. The time when the wild animals, whose furs 

 are used in commerce, acquire their winter coats, corresponds with the hunting sea- 

 son. " During the summer months the fur is thin and short, and is scarcely ever 

 an object of pursuit ; while, during the winter, it possesses in perfection all its thIu- 

 able qualities. When the beginning of winter is remarkable for its mildness, the fur 

 is loncrcr in ripening^ as the animal stands in no need of the additional quantity for 

 a covering ; but as soon as the rigours of the season commence, the fleece speedily 

 increases in the quantity and length of the hair. This ■ increase is sometimes very 

 rapid in the Hare and the Rabbit, the skins of which are seldom ripe in the fur un- 

 til there is a fall of snow, or a few days of frosty weather ; the growth of hair in such 

 instances being dependent on the temperature of the atmosphere. In the northern 

 islands of Scotland, where the shcai's ai'o never used, the inhabitants watch the time 

 when the fleece of their Sheep is ready to fall, and pull it off with their fingers. Tho 

 long hairs, which likewise form a part of the covering, remain for several weel^s. as 

 they are not ripe for casting at the same time as the fine wool. The operation c.f 

 pulling off the wool, provincially called rooiyig, is represented by some writers, more 

 humane than w^ell-informed, as a painful process to the animal. That it is not even 

 disagreeable, is evident from tho quiet m.anner in which the Sheep lie during tho 

 pulling, and from the case with which the fleece separates from the skin." 



The shedding of those antlers, which aie produced each year on the Stags, and 

 other Deer, may be explained on the same principles as the shedding of hair, and other 



external appendages. As long as the bony protuberances on the forehead of the 

 Stag continue to absorb the nutritive fluids holding phosphate of lime in solution, 

 and permit them to penetrate abundantly into the parts yet soft and gelatinous, the 

 horns grow in the form of antlers of various shapes. But when these horns, being 

 completely filled with phosphate of lime, refuse to admit anymore, the latter accumu- 

 lates in a lump at the root of the horns, and obstructs the nutritive canals. These 

 soon die, and the passage from within outwards, being thus interrupted, the antler 

 dies and falls like the withered leaf or the dead feather. 



In a similar manner we may t-xplain the shedding of the milk teeth in the Human 

 infant and the other I\Iammalia. The germs of the second teeth, before they appear 

 externally, exist at the root of the gums, in the form of small capsules, which receive 

 their nutriment from the blood-vessels of the maxillary arteries, and their sensation 

 from the dentary nerves. "When the first teeth have attained their full growth, and 

 cease to admit any more nutriment, the latter is diverted to the other germs of teeth 

 situate below. The second teeth, having thus acquired more force, expel the others 

 and assume their place. 



From these instances, it may be seen that the shedding of teeth, horns, hair, feathers, 

 or scales, is the same phenomenon of organization ; and that these bodies resemble 

 leaves, or rather those parasitical animals and plants, which draw their nutriment from 

 a body larger than themselves, on which they grow or live. So exact is this com- 

 parison, that the Hair and jN'ails maintain a separate Life on the corpse of IMan or 

 other Mammalia, and continue their growth until the dead body, by being entirely 

 decomposed, ceases to supply them %vith a nutritious lymph. 



Thus the moults and changes which living bodies undergo at the surface, in differ- 

 ent periods of their existence, depend upon the general fact that organized bodies 

 develop themselves continually from within outwards, so that the matter composing 

 them never remains the same. The nutritive particles derived from the food, after 

 being assimilated to our bodies, and incorporated into our proper substance, are ever 

 transitory, and tend to undergo decomposition and waste at the surface, so that as 

 fast as the internal organs are repaired, the vital force impels the nutrition towards 

 the exterior, where it is decomposed and finally rejected. Each portion of the indi- 

 vidual participates in the general nutrition; but besides this general life which the 

 organs enjoy in commion with the entire frame, each organ partakes of a special living 

 power, which can maintain itself distinct from the whole, or even occasion a growth 

 at the expense of the other parts. Hence each animal appendage has its special 

 birth, age, and limited duration, besides those which it derives from the entire body, 

 as we find in the organs of generation, the teeth, hair, feathers, and the leaves of 

 plants. These appendages, though developed a long time after the birth of the indi- 

 vidual, perish notwithstanding before it, and various external germs develop them- 

 selves successively. Thus, the special vital forces of particular parts possess a much 

 shorter duration than the general Life of the body. Further, these productions 

 which succeed each other, whether hair, feathers, or teeth, may neither have the samo 

 form nor colour. The radical leaves of Plants often have forms and colours very 

 different from those of the branches and floral peduncles. The feathers of the winter 

 plumage are more downy and thick than those of summer, or the nuptial period of 

 Birds. The second teeth of the Mammalia have very different roots from the for- 

 mer ; an old Stag receives a more formidable defensive weapon than the Fawn whoso 

 first horns are beginning to shoot. Thus, Nature has implanted in animals and plants 

 different kinds of germs, appropriate to the several epochs of Life, as well as tho 

 external circumstances of their situation, and even in reference to their relative situa- 

 tion in respect to the heavenly bodies. The rich variety which we find in these 

 arrangements at once demonstrates the adm-rable economy of Nature, which operates 

 incessantly in evolving or developing, according to fixed and determinate laws. Every 

 one is compelled to acknowledge that organized bodies are formed in exact corres- 

 pondence with the physical agents wdiich surround them, otherwise the harmony and 

 concourse of all portions of Nature could not subsist. Living bodies are not onlv 

 formed in direct co-relation to Air, Food, and Moisture, but also with the laws of 

 Light, excepting, perhaps, in certain subterranean animals and plants, and require 

 the influence of a moderate Heat. 



Electricity, and that form of Electricity which we commonly term Magnetism, 

 may also contribute towards the vital action in certain circumstances. So close is 

 the co-relation of Electricity with the vital power, that several later writers have 

 confounded the one agent with the other. Although it is impossible to admit that 

 Life is the same as Electricity, yet their intimate connexion is undoubted. Animal 

 bodies are in this respect delicate electro-vital machines, and acutely sensible to the 

 electrical state of surrounding bodies. 



Animal electricity has been shown by Mr Faraday to be identical with all the 

 others, only that it resides in those imperfect conductors which compose the animal 

 tissues, in the same way as Voltaic Electricity penetrates into the metallic substance, 

 and the ordinary Electricity exists at the surfaces of bodies. In fact, all these Elec- 

 tricities may be converted into each other, and Magnetism itself is only a particular 

 form of Electricity. 



There is no phenomenon among the Mammalia which can compare in intensity to 

 the electric batteries of certain Fishes. The presence of Electricity is, however, 

 demonstrated in various ways. The Hair and Skin of Man, when heated, have been 

 accompanied, under certain circumstances, by remarkable electric and luminous sparks. 

 Hales and Bellingeri have shown the different states of Electricity in tho humours of 

 the Human Body. Friction can draw electrical sparks from the Fur of the Cat and 

 several other Mammalia, chiefly carnivorous. The same thing has been found with 

 the plumage of certain Birds, as the Parrots. 



It w^as conjectured by Humboldt, and confirmed by the experiments of MM. 

 Prevost, Dumas, and Edwards, that every muscular contraction, and every act of 

 the Will or voUtion, is accom.panied by a kind of electrical discharge of the nerves 

 which animate it, and that the nerves serve to deposit and distribute an electro-vital 

 fluid. 



The scintillations and corruscatinns which emanate from the eyes of certain Blam- 

 malia when in the dark, are phenomena of a very different kind from that general 

 pho?pl:oresccnce which prevails over tho entire bodies of many Fishes, Mollusca, Crus- 



