W. J. (William J.) Miles.

Modern practical farriery : a complete system of the veterinary art as at present practised at the Royal Veterinary College, London online

. (page 149 of 160)
Online LibraryW. J. (William J.) MilesModern practical farriery : a complete system of the veterinary art as at present practised at the Royal Veterinary College, London → online text (page 149 of 160)
Font size
QR-code for this ebook


to a very considerable degree. An experiment was made on
a very large scale; 1523 sheep were vaccinated, and the dis-
ease passed through its different stages ; they were all after-
wards inoculated with the matter of sheep-pox, and in 308 of
them the disease was produced in the usual mitigated form
after this operation Other experiments were made on a
smaller scale, and with a similar result ; and therefore the
vaccine inoculation is now abandoned on the Continent,
although it gives immunity to four-fifths of those that have
been subjected to it, for inoculation with the claveau, or the
virus of the sheep-pox, will give immunity to all. There
is one disadvantage attending the use of the claveau, that it
retains its power not more than a few days, whatever care
may be taken of it. The vaccine matter retains all its pro-
perties a much longer period."



THE AGE OF THE OX AS INDICATED BY
HIS TEETH.



PREHENSION OF FOOD.

Previously to explaining the dentition of the domestic
animals under notice, it will be necessary to consider briefly
the mode by which different animals, and particularly the
ox, sheep, and pig, select and collect their food. Everybody
knows that the act of prehension varies. Man, fo^ instance,
employs his hands and mouth, and is assisted in so doing by
artificial means ; the elephant by a prolongation of the nose,
"trunk," accomplishes this act; the horse selects food with his
lips, the ox gathers it with his tongue, the sheep collects the
herbage from the pasture between his teeth, (incisors) and dental
pad, and is assisted in so doing by his tongue. Consequently
it is readily seen that several distinct organs, comprising what
is commonly called the mouth, act either by themselves or in
association with each other in the prehension of food. One
animal first grasps his food with his teeth, which is imme-
diately moved within his mouth by his tongue ; another first
collects food with his tongue, which organ conveys it to the
teeth, and among other animals the lips constitute the pre-
hensile organs; but in every case each organ assists in placing
food in the mouth, to be afterwards conveyed between the
molar teeth for the purpose of mastication and deglutition.

THE MOUTH

is bounded in front by the lips, on each side by the cheeks,
below by the tongue, above by the palate, and terminates



behind in the formation of the fauces. The mouth is lined
throughout with mucous membrane, Immediately witliin the
lips and cheeks the dental arches occur, consisting of gums
and teeth, &c. ; the gums are composed of fibrous tissue, are
closely connected with the periosteum common to the alveolar
processes, and are in adult life surmounted by teeth.

THE DENTAL PAD.

The incisor teeth, although placed in the front part of
the mouth, are variously arranged in different animals : for
instance, the pig possesses, like the horse, twelve incisors, six in
the upper, and six in the lower jaw ; the wearing surfaces of
which immediately oppose each other in the act of collecting
food. In the ox and sheep, however, a different arrangement
is presented to our notice, as in them only eight incisors
occur, all of which are placed in the lower jaw, and conse-
quently cannot oppose their grinding surfaces to teeth in the
upper jaw, as none exist. To make up for this lack of teeth,
nature has provided for these ruminants a dense cushion, the
dental pad, in the upper, to abut against the incisors situated
in the lower jaw. The dental pad is formed by the bars of
the mouth, which thicken, as they reach its anterior part, until
they concentrate in the development of the pad. The pad,
however, is of a more fibrous, elastic, nature than the bars, and
of course in this position answers the purpose of teeth; in
fact, teeth in these ruminants could not be retained in the
mouth, as the incisors in the lower jaw possess small fangs,
and are otherwise very loosely implanted in their sockets.
Moreover, the shape of the teeth does not cause them to be
capable of withstanding the effects produced by dental attri-
tion ; the ox and sheep in gathering their food can and do
employ only that force which is sufficient, and can be easily
witiistood by the teeth when meeting the yielding substance of
the dental pad. The Stenonian ducts, two in number, pass
from the mouth to the nostrils, and open on the dental pad,
and are placed there as a means whereby the odour of plants
may be appreciated by the smell, to enable the creature
possessing them to select good food from bad or poisonous
substances. The ducts of Steno have not been discovered iu
the pig, but communications between the mouth and nostrils
equally direct exist, as in the pig there is a large plexus of
nerves running down each side of the nose and ramifying over
the nostril, in which resides the peculiar power which enables
the hog to detect (or, more correctly, smell out) food buried
many inches below the surface of the ground. The olfactory
nerve, too, is large ; and although it is smaller than that of the
dog, it is much larger than the same nerve common to the ox
and sheep ; in short, the omnivorous animal the pig holds, in
this particular, an intermediate position between the herbi-
vorous and carnivorous classes.

CLEAVAGE IN THE UPPER LIP OF THE SHEEP.

The prehensile organs of the sheep are his teeth and dental
pad, assisted by his lips in a very marked and peculiar manner.
Every sheepowner knows that a sheep wUI get fat where



60



THE DISEASES OF CATTLE, SHEEP, AND PIGS.



an ox or horse would starve, i.e., the horse and ox would
waste in condition on a down, where a sheep would grow
plethoric; and this is owing to the cleft in the upper lip,
which by being pressed out from within outwards allows the
sheep to bring its teeth or dental pad much nearer to the
roots of plants than any other animal. The ox, perhaps,
with a similar division in the lip, might bite the herbage
nearly as close ; but then the thickness of the nose as com-
pared with that of the sheep, and the naked structure of it,
i.e, its being denuded of hair, would prevent that close
approximation to the ground which would be necessary in the
collection of food. Nature, however, has given to the upper
lip of the sheep a defence, in the shape of a dense coat of hair
covering the whole of the lip with the exception of the direct
fissure. By this beautiful arrangement it is almost impossible
for any foreign substance, whether it be dirt, any thick or
glutinous material, insect, or water, to penetrate to the skin.
The portion of the lip denuded of hair is small in the sheep,
as compared with the ox ; it consists of the nostrils above, and
terminates in a narrow channel which enters into the for-
mation of the cleft in the upper lip, and is usually bedewed
with moisture ; this, again, also materially assists in protecting
the lips, &c., against the invasion of foreign objects.

THE TEETH.

Generally in mammals two sets of teeth appear during the
lifetime of the animal ; the first which are put up constituting
the temporary or milk teeth, whilst those which replace them
or spring up afterwards, are named the permanent. Teeth,
although divided into several classes, present certain characters
in common ; for instance, each tooth exhibits a crown, or that
part of the tooth which projects above the gums, and immedi-
ately above and just within the gums, a constricted portion of
tooth occurs, which has been named the cervix or neck, and
below the cervix the tooth structure is lodged in the socket or
alveolus, and in this position has been denominated the fang.

The tooth fangs are accurately adapted to the alveoli; so
firmly are they fixed in their sockets, that a nail could not be
driven into a garden wall more firmly, and for this reason
the mode of union has received the name of gomphosis,
from the Greek yoficpo';, a nail. The alveolus and the fang
are both lined with a membrane which invests the external
surface of bones, and is called periosteum. This membrane
extends as high up as the neck of the tooth, and owing to its
dental arrangement, by some anatomists has been called the
periodontal membrane. Although for the sake of description
a tooth has been divided into its crown, neck, and fang, we
find in investigating the mouths of the horse, ox, and sheep,
that more than half the body of the tooth is imbedded in the
alveolus, and some of the molar teeth and tusks are in fact
destitute of fangs and necks. This fact is to be observed in
the incisors, &c., of the horse and pig.

THE TOOTH STRUCTURE.

Un making a section of a tooth, we discover that three
constituents, varying in density, and partaking somewhat of



tne character of bone, combine in forming the dental structure;
these are named — enamel, dentine, and crusta petrosa. Enamel
is the hardest; it is met with on the crown of the simple
tooth, and invests the body and sides of the compound one.
In the centre of a tooth a cavity occurs, which is called the
pulp cavity, which during life is filled with a highly vascular
and sensitive organism, the dental pulp, supplied with blood-
vessels and nerves which enter the tooth by means of a small
orifice at the point of the fang. The size of the pulp cavity
depends upon its age, being always large in young animals,
but decreases in size as age advances : this cavity is lined by
dentine. " On inspecting an incisor of an ox, we observe that a
white incrustation, having in the young subject more or less ot
a pearly white appearance, covers the crown of the tooth ; this
is enamel. If the tooth should have been recently put up, this
substance forms also its cutting edge. It is thicker on the
front surface of the crown than on the back, an arrangement
which tends to keep up a sharp edge to the tooth ; it extends,
also, downwards to the neck, where it ceases. The enamel
not only covers the exposed surface of a tooth, but in some
teeth it enters deeply into their interior. It matters not what
may be the size or shape of a tooth, or how numerous its
projections, the whole of these are originally covered with a
layer of enamel. Microscopically enamel has been discovered
to be composed of several rods lying side by side, named
enamel prisms or fibres, which always rest their ends upon
the dentine to which they are immediately attached. Minute
canals, also, have been detected in the enamel recently formed,
the use of which is explained by Professor Simonds : — " In
looking to the situation of enamel in compound teeth, it is
stated that this structure dips inwards, forming cups of greater
or less depth in different teeth, and which are always filled
with crusta petrosa. On the slightest reflection we perceive,
that the crusta here placed can only receive the fluid necessary
for its support through the layer of enamel which is interposed
between it and dentinal tubes ; and there seems no reason to
doubt that the tubes, from the boundary of the dentine, may
extend to the canals between the prisms, and thus supply
the materials of nutrition to the crusta petrosa within
the cup. Mr. Tomes, many years since, drew attention to
the fact that dentinal tubes passed in great numbers into the
enamel of the Kangaroo and other animals of this class.
From my own examinations I can also say that the dentinal
tubes penetrate the enamel in the Herbivora ; and it is more
than probable that in consolidated enamel the passages
referred to are united with these dentinal tubes, and thus
become consolidated with them."

Todd & Bowman, in their work on Physiological Anatomy,
support this view, that the enamel prisms " are arranged in the
most suitable manner for the percolation of the fluids derived
from the dentinal tubuli. These tubuli, indeed, may be seen
to commimicate directly with the interstitial passage of the
enamel." Enamel, when subjected to the action of dilute acids
yields scarcely any trace of animal matter, but contains carti-
lage, and not more than two-tenths of organic matter (apparently



THE DISEASES OF CATTLE, SHEEP, AND PIGS.



61



membraneous tissue), in the enamel of the human tooth. Ber-
zelius found —

Phosphate of lime with flnoride of calciam, 88°6

Carbonate of lime, ..... 8'5

Phosphate of magnesia, . . . . 1'6

Membrane, alkali, and water, . . . 2'0

100

Nearly similar results have been obtained by Von Bibra and
Frfemy. The former chemist found as much as four-tenths of
fluoride of calcium in enamel.

Second in density to enamel is the ivory tooth substance, or
dentine, which principally forms the mass, and gives the gene-
ral configuration of the tooth structure. Dentine diflFers little
from bone in appearance, but is not identical with it in struc-
ture ; for although it appears to the unassisted vision to possess
a compact subsistence, by the assistance of the microscope it
is found to be composed of numerously arranged fine tubes
(the dental tubuli), which terminate at their inner ends by
minute orifices opening into the pulp cavity. These tubes
describe a wavy course, which split into branches ; first into
two, and by further separation numerous ones are formed,
which ultimately terminate in very fine inosculating branches.
" Towards the terminal portion of the fang the dentinal tubes
in some animals, of which the sheep is an example, are col-
lected into little bundles, having between them a comparatively
large space, which is occupied by the intertubular substance."*

The intertubular substance is translucent and finely granu-
lar. Henle describes the animal basis which remains after
the substance has been treated by an acid, " as separable into
bundles of pale, flattened, granular fibres, running in a direction
parallel with the tubes;" and Nasrayth "that it consists of
brick-shaped cells, built up as it were around the tubules."
Dr. Sharpey disputes both these assertions, which are in oppo-
sition to observations that have been made in reference to the
cachalot and sperm whale, in which the animal substance
can readily be torn into fine lamellae, " disposed parallelly with
the internal surface of the pulp cavity, and therefore across the
direction of the tubules." Moreover, the laminated structure
of the dentine has been noticed by Salter and Czermak in the
human tooth.

The chemical composition of dentine is very similar to that
of bone ; the quantitative ratio between the organic and inor-
ganic constituents approximating very closely to that occurring
in the denser bones, and averaging 28'72. From 3 to 8 tenths
of carbonate of lime has been found, with from 65 to 67 tenths
of the phosphate of lime, together with a little of the fluoride
of calcium and phosphate of magnesia.

The third substance entering into the tooth formation is
crusta petrosa, which closely resembles bone, both in its
physical and chemical character, althougli it is slightly modi-
fied in structure. Crusta invests the entire fang of the tooth,
and those parts of the dentine which are devoid of enamel.
The quantity of crusta present depends more upon the char-
acter than the size of the tooth, owing to which we find crusta

• Simonds on the Formation of the Teeth.



more largely developed on a compound than on a simple
tooth, for the reason that this substance covers only the fangs
in simple teeth, whereas it not only invests the fangs, but
also covers with enamel the interior organization of com-
pound ones.

As age advances the crusta grows thicker, especially at the
apex of the fang, and sometimes is developed then to such an
extent as to block up the orifice through which the nerves
and bloodvessels pass to the pulp, for the support of the dental
structure.

Under the microscope crusta is found to resemble bone, as
it possesses cells, " lacunae," from which minute canals emerge,
called canaliculi, which anastomose with the terminal tubules
of the dentine. Where the crusta is thick, numerous vascular
canals occur, similar to the Haversian canals of bone.

On the fangs of teeth recently cut, little crusta is discovered
when compared with that existing on old teeth. It may never-
theless be asked how the increased quantity upon old teeth
is accounted for? Professor Simonds accounts for this diffi-
culty as follows : — " I premise the explanation of this matter
by stating, that anatomists are generally agreed that, after a
given time, the pulp ceases to produce any more dentine, and
becomes converted by ossification into a substance which Pro-
fessor Owen designated osteo-dentine. This substance, there-
fore, would now fill the pulp cavity of the tooth. However
true this statement may be of man or many species of animals,
it does not appear to be positively correct when applied to our
domesticated Herbivora. In the horse, as an example, oblit-
eration of the cavity is gradually effected by the pulp continu-
ing to form dentine. This, as its normal action, goes on, and
is not supplanted by an abnormal or diseased one, as it would
be were the pulp to become ossified. As the producing organ
of dentine, the pulp simply gives way to its own product,
which is ultimately made to occupy its place in the cavity.
In proportion as the pulp diminishes, so is the supply ot
nufriment to the tooth lessened, and at length entirely cut ofl
from the interior. To provide for the vitality of the tooth
under these circumstances, the crusta increases in quantity on
the fang, at the expense of the perfectly formed dentine which
is lying in immediate contact with its inner surface. Through
the medium of the canals of the crusta, which open on its
border, the tooth now draws its nourishment from the blood-
vessels of the socket, and thus it continues, long after the
obliteration of its pulp cavity, to serve aU its purposes as a
part of the living organism."

Crusta petrosa chemically seems to be almost identical with
bone. The researches of Lassaigne and Von Bibra, on the
teeth of different animals, could detect no definite difference
between the teeth of herbivorous and carnivorous animals.

THE DEVELOPMENT OF TEETH.

In considering the mode by which the teeth are formed, it
is necessary to commence with a description of their creation in
foetal life ; for we find that, even so early as this period, indi-
cations not only of the temporary or deciduous te3th, but aUo



m



THE DISEASES OF CATTLE, SHEEP, AND PIGS.



of the permanent ones, or those which succeed them, exist.
This process in the human foetus. Professor Goodsir asserts,
begins about the sixth week.

For the sake of description, we must first explain the origin
and gi-owth of teeth, and afterwards the mode by which their
eruption in two sets, namely, the temporary and permanent
sets, takes place. The process of dental formation has been
divided into four separate stages, namely — 1st, the papillary;
2nd, follicular ; 3rd, saccular; and 4th, eruptive ; and from the
researches of eminent physiologists it is certain, that teeth are
developed from the mucous membrane covering the bones in
opposition to them. Professors Goodsir and Arnold discovered,
independently of each other, that the first stage of development
consisted of certain changes in the mucous membrane, and
that about the sixth week in the life of the human foetus a
depression or groove, having " the form of a horse shoe," was
noticeable "in the mucous membrane of the gum," named
by Professor Goodsir the " primitive dental groove." This
groove is lined by the membrane of the mouth, which con-
sists of two layers almost identical with the epidermis and
dermis of the cutis, or skin proper. From the floor of the
dental groove papillae spring up, which constitute the early
formations of the dental pulps about to belong to the milk or
temporary teeth ; in the ox, for instance, eight papillae in the
lower jaw, and twelve in the upper and lower jaws, indicate
the situations of the eight incisor teeth in the former, and the
twelve temporary molars in the latter. Concurrently with
the growth of tlie papillae bony partitions spring up, which
form a " series of four-sided cells," and by subsequent growth
these cavities, called loculi, become established, when they are
named alveoli. This formation of the papillae constitutes the
papillaiy stage. The papillary stage is succeeded by the
follicular, which consists in the thickening and prominence of
the dental groove, and the prolongation of the mucous mem-
brane, which forms for each papilla a distinct cavity called a
follicle, and, as time advances, grows so deep as to hide the
papilla which corresponds to the shape of the future teeth ;
and now the edges of the dental groove begin to approach
each other, and ultimately join, and thus close up the entrance
to the cavity; and in so doing form a closed sac, at which
time the saccular stage is said to be completed.

The fourth or eruptive stage, as it occurs in the human
gums, is, as follows, very distinctly explained in Dr. Quain's
" Anatomy," edited by Doctors Sharpey and Ellis : —

" The dental sacs formed by the closure of the follicles con-
tinue to enlarge, as well as their contained papillae. The
walls of the sacs, which soon begin to thicken, consist of an
outer fibro-alveolar membrane, and an internal highly vascular
layer, lined by epithelium ; thin bloodvessels are derived
partly from the dental arteries, and partly from those of the
gums. The papilla, now the dental pulps, adhere by a wide
base to the bottom of the sacs, but are unattached elsewhere ;
and having acquired a perfect resemblance to the crowns of
the future teeth, the formation of the hard substance com-
mences in them. This process begins very early, and by the



end of the fourth month of foetal life thin shells or caps oi
dentine are formed on all the pulps of the milk teeth, and a
little later on that of the first permanent molar. The mode
in which it proceeds, taking a canine tooth as an example,
may be stated as follows : — A thin osseous shell or cap of
dentine appears on the point of the pulp; this increases in
extent by a growth around its edges, and in thickness by a
similar formation in its interior, the latter taking place at the
expense of the substance of the pulp itself, which accordingly
decreases in proportion. This growth of the tooth continues
until the crown is completed of its proper width, and then the
pulp undergoes a constriction at its base to form the cervix
of the tooth. From that time the pulp elongates, and con-
tinues to become narrower, so as to construct the fang.
During the whole period another process has been going on,
by which the outer surface of the crown is covered with
enamel. This substance is formed from a peculiarly organized
body lying on the pulp, and accurately adapted to its surface
and to its cap of dentine, and which was called by Hunter the
outer pulp. Sooner or later after the completion of the crown
this part of the tooth appears through the gum, whilst the
growth of the dentine to complete the fang is continued at
the surface of the elongating pulp, which gradually becomes
encroached upon by successive formations of hard substance
until only a small cavity is left in the centre of the tooth,
containing nothing but the reduced pulp, supplied by a slender
thread of vessels and nerves which enter by a little aperture
left at the point of the fang after the dentine is completed.
In the case of teeth having complex crowns, and more than a
single fang, the process is somewhat modified. On the sur-
face of the dental pulp of such a tooth, as many separate little
shells of dental substance are formed as there are eminences
or points; these soon coalesce, and the formation of the tooth
proceeds as before as far as the cervix. The pulp then
becomes divided into two or more portions, corresponding
with the future fangs, and the ossification advances in each as
it does in a single fang. A horizontal projection or bridge of
dentine shoots across the base of the pulp, between the com-
mencing fangs ; so that, if the tooth be removed at this stage,
and examined on its under surface, its shell presents as many
apertures as there are separate fangs. In all teeth the pulp
originally adheres by its entire base to the bottom of the sac;
but when more than one fang is developed the pulp is, as
it were, separated from the sac in certain parts, so that it
comes to adhere at two or three insulated points only, whilst
the dentine continues to be formed along the intermediate and
surrounding free surface of the pulp." From this descrip-
tion it will be readily understood, that immediately after the
crown of the tooth has penetrated the sac and gum, the erup-



Online LibraryW. J. (William J.) MilesModern practical farriery : a complete system of the veterinary art as at present practised at the Royal Veterinary College, London → online text (page 149 of 160)