ocr to tei v2 animals three pages

v2_animals_pages.xml

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			<p>
CHAPTER I.
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<p>
ANIAIAL STRUCTURE AND FUNCTION.
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<p>
A KNOWLEDGE of the Structure of the various parts of the body<lb/>
{aiiato7ny) and the functions they performi {physiology)^ provides a<lb/>
rational foundation on which to base our acquaintance with animals,<lb/>
their requirements and capabilities ; and so that all may get a clear idea<lb/>
of these complex and technical subjects, necessary references to them<lb/>
are given in as simple language as possible.
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<p>
Cells. — All animal bodies are composed of cells. A cell is a minute Cells,<lb/>
round mass of living matter, which may or may not possess the property of<lb/>
moving itself. Though at first all cells appear alike, they soon become<lb/>
specialised to perform one particular duty, e.g.^ the liver cell makes bile ;<lb/>
the muscle cell acquires the power of contraction. As they increase in<lb/>
number, the pressure of surrounding cells causes them to alter in shape<lb/>
and they may become many sided, flat or spindle-shaped. The entire<lb/>
animal is made up of such minute, specialised bodies, a single cell<lb/>
bearing the same relation to the whole body that a brick does to<lb/>
London. Cells multiply by dividing, each portion attaining to the size<lb/>
of its parent. This power is most marked in youth, growth^ and<lb/>
declines in age, decay.
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<p>
Bones. — The framework of the body is constructed of bones^ so Bones,<lb/>
arranged that they can be used as rigid supports, or become freely<lb/>
movable when the joints are brought into play. A joint is formed joints,<lb/>
wherever two bones meet and move over each other ; it is always<lb/>
surrounded by an air-tight capsule, and in order to prevent any friction,<lb/>
the ends of the bones are covered by thick layers of gristle {cartilage\<lb/>
which have extremely smooth surfaces. Inside the joint are found special<lb/>
fringes which lie loosely in the capsule and produce "joint oil " {synovia), a<lb/>
peculiarly oily, slippery fluid, which bathes the entire joint and ensures<lb/>
the most perfect lubrication. The movement of joints is accompHshed<lb/>
by the action of muscles.
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<p>
Muscles are the red butcher's meat which we eat, constitute a great Muscles,<lb/>
part of the body, and are attached to the bones in such fashion as to
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			<p>
ANIMAL MANAGEMENT.
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<p>
enable them to move the joints to the greatest advantage when they<lb/>
contract. The power of contraction is the distinguishing feature of<lb/>
muscles : when called into action tKey shorten and thicken themselves,<lb/>
drawing their points of attachment closer together and so bending the<lb/>
joints.
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<p>
In addition to the red muscles {voluntary) with which we are all<lb/>
familiar, and which we move at will, there is another set not under the<lb/>
control of the will {involuntary), which is met with throughout the<lb/>
internal organs, and to which, in particular, the bowels owe their<lb/>
remarkable power of movement. These involuntary muscles, except the<lb/>
heart, are pale in colour and distributed in thin layers instead of thick<lb/>
bunches ; but they are as powerful and capable of even more<lb/>
sustained exertion than the voluntary ones. In speaking of muscles<lb/>
generally, it is the red, voluntary ones which are alluded to, but the<lb/>
existence of the others should not be forgotten.
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<p>
Te/idons. — Muscles, though very elastic and capable of exerting great<lb/>
force, are quite soft and easily torn ; they would be incapable of<lb/>
withstanding the strains to which they are constantly subjected if they<lb/>
were not provided with tendons. A tendon is a tough, inelastic rope,<lb/>
composed of firm, parallel threads, running throughout its length, one<lb/>
end being securely attached to a bone, whilst the other is spliced into<lb/>
the substance of a muscle. Through the medium of this rigid attachment<lb/>
the muscle exerts the full force of its elasticity without fear of injury and,<lb/>
as a matter of fact, when sprains of these structures do occur, it is<lb/>
usually the tendon which gives way.
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<p>
Ligaments are similar in structure to tendons, but differ in their<lb/>
attachment ; they run from bone to bone in the neighbourhood of joints,<lb/>
and are not attached to muscles. They serve to prevent over-extension<lb/>
of joints, and while permitting free movement, knit the component bones<lb/>
firmly together.
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<p>
The Nervous System. — The whole of the above organs of locomotion<lb/>
are set in action and controlled by the will power, which originates in the<lb/>
brain and is transmitted by means of the spinal cord and nerves. The<lb/>
Nervous inechanism maybe aptly compared to a very complete telephonic<lb/>
system which, radiating from the central exchange, the brain, takes orders<lb/>
and conveys messages to and from the entire body. Nerves may be<lb/>
divided into two groups, those which gives rise to feeling {sensory), and<lb/>
those connected with motion {?/iotor).<lb/>
The spinal The Spinal Cordis the continuation of the brain down the back-bone,<lb/>
cord. from which many nerves arise, and which acts the part of sub-office to
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<p>
the brain.
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<p>
Liga-<lb/>
ments,
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<p>
The
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<p>
nervous
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<p>
system.
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			<p>
ANIMAL STRUCTURE AND FUNCTION. 7
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<p>
Fat is stored in various situations to form cushions, to round off Fat.<lb/>
corners, and to serve as a reserve of food if required.
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<p>
Noicrishmeilt is brought to the whole of these structures by the blood Use of<lb/>
constantly circulating through the blood-vessels^ which are of three Blood;<lb/>
varieties, arteries^ veins^ and capillaries.
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<p>
Arteries are muscular, thick-walled elastic tubes which, springing Arteries,<lb/>
from the heart, ramify through the entire body. Gradually diminishing in<lb/>
calibre as their length increases, they reach and supply every organ and<lb/>
structure, finally becoming merged in the capillaries.
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<p>
Capillaries are, as their name denotes, the finest, thinnest, hair-like Capil-<lb/>
tubes imaginable. They permeate every nook and cranny of the system, laries.<lb/>
so that the merest pin prick will draw blood, z&amp;gt;., wound several of them.
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<p>
Veitis are the continuation of the capillaries on the return journey Veins,<lb/>
towards the heart, approaching which they increase in size, receiving fresh<lb/>
tributaries from all parts, till they empty themselves into that organ.<lb/>
Here and there in the course of a vein, slight enlargement of its calibre<lb/>
may be noticed, due to the presence of valves which prevent the blood<lb/>
flowing backwards. A valve consists of two or three little skin-like<lb/>
pouches with their openings towards the heart ; so long as the blood<lb/>
flows in that direction they lie flat against the side of the vessel and do<lb/>
not obstruct it, but if there is any back wash it automatically fills them,<lb/>
causing them to bulge into the vein and completely block it. Their<lb/>
action may be well observed by pressing the blood to and fro in the veins<lb/>
on the back of one's own hands. Veins are thinner and are less elastic<lb/>
than arteries, but are capable of containing more blood when distended.
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<p>
The Blood consists of a straw-coloured fluid, in which an infinite The blood,<lb/>
number of minute bodies {corpuscles) are suspended. During life and<lb/>
when freshly drawn from the body, blood is quite fluid, but rapidly<lb/>
solidifies {clots) on exposure to the air. The blood co7piiscles are of two<lb/>
varieties, red and white. Red corpuscles are very numerous, give the<lb/>
blood its colour, are shaped like a quoit with a solid centre, and measure<lb/>
about 3^ of an inch in diameter. Their peculiar power of absorbing<lb/>
oxygen makes them important factors in questions of ventilation and<lb/>
breathing. White corpuscles are comparatively few in numbers as<lb/>
compared with the red variety, are larger, have the power of moving,<lb/>
and are engaged in the duty of attacking and destroying any harmful<lb/>
germs which attempt to invade the body.
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<p>
The Heart is a hollow, cone-shaped organ, composed entirely of The heart,<lb/>
muscle. It is situated in the centre of the chest with its point directed<lb/>
downwards and slightly inclined to the left. Internally it is divided into<lb/>
four compartments, those on the left side being thicker walled and
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