76 
FIRST CLASS OF THE VERTEBRATED ANIMALS. 
The changes of ail these bodies partake more or less of the same general character. 
A tree may be considered as a body composed of an infinite number of germ.s wliich 
are successively developed. Besides the fruit produced each year, it pushes forth an 
immense number of loaves, which extract their nutriment from the sap, expand, and 
uirive at their full growth. Then having received all the nutriment which the ariolse 
of their tissuo 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 aud obstruction, and the leaf falls. This is observed generally in autumn 
with the trees of our climates, and happens altm in the ever-grecn trees, the only 
difference being, that in these the new leaves are repaired as fast as the old ones 
fall, so that the tree is not at any one time completely destitute of verdure. 
The same thing happens witli the feathers of Birds, and the hair of the Mam- 
malia. The bulbou-s root of the hair is penetrated by a blood-ves.sel, and that portion 
of nutriment and growth necessary to its development is thcncc 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. Thus 
the hair is a kind of plant, which has its bulb or root, and its shaft or stalk, com- 
posed of long shcathy tunics, one within another, like the tubes of a telescope. 
The casting of hair among the Mammalia arrives at differ cut 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 reqmsitc 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 tlie animals of warm regions in its quantity, but in its 
arrangement. U we examine the covering of Swine of waj*m countries, ave find it 
consisting 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 tlie 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 long hairs, which give to it, wlien 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 Northern 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 lived, and where they became at last enveloped in Ice. Had they been 
transported by any accident from a warmer region, they would haro exhibited in the 
thinness of their covering, unequivocal marks of the climate in which they were reared. 
By means of this arrangement, in reference to the quantity of clothing, individuals of 
the same species can maintain life comfortably, in climates which ditfer considerably 
in their average annual temperature. By the same arrangements, the individuals 
residing in a particular district arc able to provide against the varying temperature 
of the seasons. The covering is diminished during winter, and increased in summer, 
as may bo 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 th.m 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 likewise 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, aud the animal be- 
comes sleek ; and the warm covering of winter is excliangod for a lighter and more 
commodious garb. The Sheep in our climates casts its fleece before the end of June, 
aiid the Mole about the end of hjay. The time when the wild annuals, whose furs 
are used in commerce, acquire their wnnter coats, corresponds with tho hunting sea- 
son. “ During the summer months the fur is thin aud short, and is scarcedy ever 
an object of pursuit ; Avhile, during the winter, it possesses in perfection all its valu- 
able qualities. ^Vhen the beginning of winter is remarkable for its mildness, thelur 
is longer in riperjirifft as the animal stands in no need of the additional quantity for 
a covering; but as soon at the rigours of tho season commence, the fleece speedily 
increassa in the quantity and length of tl.e 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 weatlier ; the growth of hair in such 
instances being dependent on the temperatoro of the atmosphere. In the northern 
idamls of Scotland, where the n/iears are never used, tho inhabitants watch the time 
when the fioeco of their Sheep is ready to fall, and pull it off with their fingers. The 
long hairs, wliich Ukewise form a part of ihe covering, remain for sover-al weeks, as 
thev arc not ripe for casting at the same time as the fine wool. Tho operation of 
puUlng off the wool, provincially called rooinr/, is represented by some writers, more 
liumane than wcll-iiiforraed, as a painful process to the animal. That it is not even 
disagreeable, is evident from tho quiet manner in which the Sheep lie during the 
pulling, aud from tho ease with which the fioecc separates from the skin. 
The shedding of those antlers, which are produced each year on tho Stags, and 
oth'T' I'ecr, may be explained on the same principles 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 yt»t soft and gelatinous, the 
horns grow in tho 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 explain the shedding of the milk teeth in the Human 
infant and the other Mammalia. 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, tho 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 Nails maintain a separate Life on the corpse of Man or 
other Mammalia, and continue their growth until the dead body, by being entirely 
decomposed, ceases to supply them with 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 outwanls, so that the matter composing 
them never remains the same. 'J'hc nutritive parlioles dt-rivod from the food, after 
being assimilated to our bodies, and incorjioratcd into our proper substance, are ever 
transitory, and tend to undergo decomposition and waste at tho 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 common 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 h-ns 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. Those appendages, though developed a long time after tlie 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 tho general Life of the body. Further, these productions 
w hich succeed each other, whether hair, fi'athers, or teeth, may neither have the same 
form nor colour. The radical leaves of Plants often have forms and colours very 
different from those of the branches and floral peduncles. Tlie featliers 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 whose 
first horns are beginning to shoot. 1 hus, Nature has implanted in animals and plants 
different kinds of germs, appropriate to the several epochs of Life, as well as the 
external circurastauces 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 admirable 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 arc formed in exact corres- 
pondence with the physical agents which surround them, otherwise the harmony and 
concourse of all portions of Nature could not subsist. Living bodies are not only 
formed in direct co-relation to Air, Food, and Moisture, but also with the laws of 
Light, excepting, perhaps, in cenain 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 tho 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 al! the 
others, only that it resides in those imperfect conductors which compose the aninial 
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 BelUngeri have shown the different states of Electricity in the humours of 
the Human Body. Friction can draw electrical sparks from tho 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 was conjectured by Humboldt, and confirmed by tho experiments of 
Prevost, Dumas, and Edwards, that every muscular contraction, and every act of 
tho Will or volition, is accompanied by a kindnf electrical discharge of the nerve* 
which animate it, and that the nerves servo to deposit and distribute an clcctro-vH'** 
fluid. 
1’ho scintillations and corruscations which emanate from the eyes of certain P'frm- 
malia when in the dark, arc phenomena of a very different kind from that gem’ra 
pi*, isphorcsccnce which prevails over the entire bodies of many Fishes, Mollusca, Cru< 
