8 
THE ORGANS OF ANIMAL BODIES— THEIR FUNCTIONS. 
If these arteries be irritated in an unusual degree, they act more forcibly 
and propel a greater quantity of blood; the nervous fluid becoming more 
abundant, increases the local sensibility; and, reacting upon the irritabi- 
lity of the arteries, carries their mutual action to a high degree. This is 
called nervous excitement, or orgasm; when it becomes painful and per- 
manent, it is termed injiammaiwu. 
'riiis mutual influence of the nerves and muscular fibres, whether in 
the intestinal or arterial systems, is the true source of those involuntary 
actions, common both to plants and animals. 
Each internal organ is susceptible of irritation only from its peculiar ir- 
ritant, to which it is in a manner especially adapted, just as an exter- 
na! sense can be affected only by its particular objects. Thus mercury 
irritates the salivaiy' glands, and cantharides, the vesica. These agents 
have been called specifics. 
As the nervous system is continuous and of uniform structure, local 
irritations, and frequently repeated sensations, fatigue it throughout the 
whole extent; so that any function, when excessively exercised, may en- 
feeble all the others. Thus, too much food impedes the action of the 
intellectual powers, and long protracted study impairs the powers of di- 
gestion. 
An excessive local irritation may affect the w’holo body, just as if all 
the vital cuo gies were concentrated upon one single point. But a se- 
cond irritation, in another place, will diminish the first, or, as it has been 
called, determine the first into another part; such is the effect of blisters, 
laxatives, and other counter-irritants. 
Wc have thus shown, in the above brief sketch, tliat it is possible to 
account for all the phenomena of physical life; if we merely assume hy- 
pothetical! v the existence of a nervous fluid, possessed of certain proper- 
ties, which are deduced from generalizing the phenomena of the vital 
s}'.stem. 
SKCT. VI THE ORGANS OF ANI.M.VL BODIES, THEIR APPROPRIATE FUNCTIONS, 
WITH THEIR VARIOUS DEGREES OF CO.MPUCATION. 
Siuxation Touch — Tarte — Smell — Sight ^ TTearing — Muscular Sciuc — Head — 
Praia Voluittarg Motion — Muscles — Boyies — Tendons — Ligamcntr — Nutrition 
Stomach Gastric Juice — Chyme — Chyle — Lacteuls — Arteries — eins — 
Lymphatics — Respiration — Lungs — GUIs — Trachea: — Capillary Vessels — Se- 
cretory Glands — Generation. 
After having considered the organic elements of the animal body, the 
chemical elements of its composition, and the active forces which prevail 
in it, nothing now remains to complete a general view of the animal sys- 
tem, excepting a summary account of the several functions of which life 
is composed, with a description of their appropriate organs. 
Tile functions of the animal body may be divided into two classes — the 
animal functions, which are peculiar to animals — and the vital or vegeta- 
tive functions ; common to animals and plants. The former comprise sen- 
sation and voluntary motion, the latter nutrition and generation. 
We shall commence with sensation, which resides in the nervous 
sy.'tcm. 
The sense of touch is the most extensively diffused of all the external 
senses. It is seated in the skin, a membrane enveloping the entire body, 
and traversed in every part by nerves. Their extreme fibres are ex- 
panded at the surface of the^ skin into minute papilla:^ or small project- 
ing filaments, where they are protected by the outer skin, and by other 
insensible coverings, such as hair or scales. 
The degree of perfection in which different animals possess this sense varies consi- 
derably; but its exercise, in a high degree, is always accompanied by certiun conditions. 
The organ must be supplied with numerous nerves and papill®, under a very fine cu- 
ticle; with a soft cellular substance, like a cushion; .and with a hard Resisting base. 
It must also be endowed with, a con.sitlerable degree of flexibility, as a close contact 
witli the surfaces of bodies is indispensable. Most animals arc possessed of some par- 
ticular organ, in which the sense of touch is developed in a high degree. In tho hand 
of man, and particularly at the extremities of the fingers, we find all the necessary 
reqiujiites of this sense, combined in their most perfect form. The proboscis, or trunk, 
of the elephant seems to rank next to the human hand; and, among the higher orders 
of animals, either tho snout or tho Up is endowed with much semibility. This 
quriity is particularly observable in the nose of the tapir, and of the hog, in the 
lips of the mole, and in the upper Up of the rhinoceros. Tho seal, and animals of the 
cat kind, such as the lion and tiger, have whiskers, possessed, near their roots, of consi- 
derable deUcacy, which renders them of important use to these animals as feelers. Cer- 
tain species of monkeys have delicate prehensile tails, which they use with surprising 
agility. In birds, the nerves of touch seem chiefly developed in the feet and toes, 
and most of the aquatic species are endowed with bills of considerable feeling. Ser- 
ponrs use their slender tongues as instruments of touch ; and the great flexibility of 
their bodies renders them well adapted for the exercise of this scue. The snouts 
of fishes have some nicety ; but, with this exception, these animals seem nearly desti- 
lule of delicate sensation. Insects feel chiefly by means of their antennse; and the 
several tribes of annelida, actinicC, and polypi, by their tentacula. Several animals 
are covered with a dense integument, in many of their parts, which arc thus wholly 
unfitted for this sense. The thick hides of the elephant and rhinoceros, the feathers 
of birds, the scales, horny coverings, and shells of the lower animals, arc evidently 
inconsistent with the necessary conditions of touch. Bats are enabled to fly in the 
darkest places, by the extreme acuteness of their tactual nerves. 
Taste and smell are merely more delicate modifications of this sense, 
for the exercise of which tlie membranes of the tongue and nostrils are 
snecially organized. 
In most of the lower animals the sens© of taste is very imperfect, or it is altogether 
wanting. The tongue of man is supplied with numerous papillx, of a conical form 
and spongy texture, projecting in a manner visible even to the naked eye. Taste 
seems in liiin to attain its mo.Ht perfect state; and ho not only enjoys the natural va- 
ricties of an omnivorous animal, but also a number of acquired tastes, which other 
species are wholly denied. The tongues of birds, of reptiles, and of fishes, are often 
covered with a hard and horny cuticle, which renders them altogether unfit for the 
delicate exercise of this sense. Many animals swallow their food without mastication ; 
an I they must be thereby effectually deprived of the enjoyments of taste, as a certain 
degree of contact between the food and the organ is essentially necessary for its exer- 
cise. 
The sense of smell resides in an organ, rendered susceptible by tho ex- 
treme delicacy and extent of its ever humid surface. 
Very minute particles of an odoriferous .substance arc darted forth in cverv diroo- 
tion, and are received upon the extensive and complex membrane, wliicli lines the in- 
ternal parts of the nasal cavity. Matter is thus perceived, when in a stale of great 
subdivision, with a degree of acuteness far surpassing any of the other senses. The 
extreme minuteness of these particles may be inferred from tlie fact, that musk, and many 
other substances, will exhale odour for several year.®, and yet no loss in their weight 
can be detected, even by the most delicate balances. Carnivorous animals, in general, 
possess a more acute sense of smell than those living upon vegetable food ; and the struc- 
ture of their nasal cavities is consequently much more intricate. This power was ob- 
viously given to facilitate the discovery of their food. In man the sense of smell seems 
best adapted for vegetable effluvia. A dog, though surpassing him in detecting tho 
most minute effluvium of another animal, will derive no pleasure from the finest 
vegetable odours. M. Audubon is of opinion that birds of prey are not endowed 
with an acute sense of smell. The degree in which this sense is enjoyed by the lower 
tribes of animals has not yet been completely determined, but it is observed to exist in 
bees and snsuls. 
The beauty of the eye, and the unbounded sphere which it exposes to observation, 
give to tho sense of sight a decided pre-eminence. Light, when emitted from the sun 
or any luminous body, strikes upon the external covering of the eyeball. By means 
of the crystalline lens, it is then refracted or bent from its original direction to a focal 
]romt, from which the rays of light are again distributed on the expanded extremity of 
the optic nerve, prepared to receive them. The size of the eyes in quadrupeds, and 
the iniensity of their vision, hear a constant relation to the nafire of tlieir food. Her- 
bivorous animals, such as the elephant and the rhinoceros, have very small eyes in 
comparison with their entire hulk. The eyes of the whale, when viewed singl}*, arc 
very large; biit they seem disproportionately small, if we contrast them with the 
enormous mass of the entire body. But quadrupeds and birds feeding on flesh, require 
powers of vision of very great intensity. In these animals wc accordingly find the 
organ large, and highly developed, so as commonly to impart a pccnliar expression of 
ferocity to their countenances. The animals which are the objects of pursuit arc fre- 
quently supplied with acute vision, thereby enabling them to escape or avoid danger; 
and this is particularly exoraplifiod in the squirrel, the rat, the deer, and the hare. 
Animals which burrow under ground, as the mole and the shrew-mouse', have, 
in general, exceedingly small eyes; while in some they have been found nearly want- 
ing, as in the blind rat (^Mus typhlusy Linn.) Tlic cat, the lemur, and other animals 
which pursue their prey during the night, are peculiarly ailaptod, by the construction 
of their eyes, for acutely perceiving objects, w’hen illuminated by a very small quantity 
of light. Tiie eyes of reptiles and fish are accommodated to the medium in which 
they reside. The chameleon can move one eye with rapidity, and in various direc- 
tions, while tho other remains fixed. Reptiles residing generally in the water, also 
fish, and the cetacea, such as the dolphin and seal, have their eyes covered with a 
dense skin, and the lens is more convex than in other animals. The arachnides, or 
spiders, possess generally eight eyes, arranged upon the upper part of the head in a 
symmetrical form ; and there are not less than twenty-eight in the common millopcdc 
(Jnlxis terrestns.) The insect tribes enjoy great variety and intensity in their visual 
organs ; but the precise limits of this sense among the lowest animals in the scale of 
creation is not yet clearly ascertained. 
The organ of hearing is excited by vibrations or undulations of air, of water, or 
of some solid medium, recurring at intervals, with different degrees of frequency* 
These impulses are received upon the tympanum or ear-drum ; thence they are com- 
municated to the acoustic nerve, and arc finally transmitted to the brain. 'When the 
vibrations are not performed in equal times, or do not occur more frequently than 
seven or eight in a second, there is heard merely a noise. But when they rise much 
above this velocity, a very low or grave musical note is first heard. By an incre850 
of velocity, the note becomes higher or more acute, and the oar is finally capable uf 
perceiving sounds resulting from 31,000 impulses in a second. There is a regular 
gradation among animals in the perfection of the organ of hearing, but none of them 
can-rival the delicacy with which the practised car in man perceives minute changed of 
tone, alterations in the quality or expression of sound, and varieties in its intensity 
loudness. Feeble and timid quadrupeds generally have their ears directed backwards, 
to warn them of approaching danger; while, in the predaceous tribes, the cars aro 
