« AnteriorContinuar »
From its presence and large development Although the teeth form so prominent in dogs, it has been called the canine and distinguishing a feature of all the fulltooth. Between these teeth, on each side, grown individuals of the higher forms of we have four teeth which have neither the animals, yet most of these animals, includbroad surfaces of the grinders, nor the ing man, are born without any teeth at all. points of the cuspidati; but they are flat, When the child is born, the jaw is covered having a sharp edge like a knife, hence with gums, but underneath the gums are they have been called incisors (d), or culting little cavities in which the teeth are formed; teeth.
and as they go on growing, they at last press Now these three sets of teeth, which we upon the .gum, and causing it to absorb may call grinders, tearers, and cutters, finally break through it. This process is represent three classes of teeth amongst the called dentition. It is frequently a source lower animals.
of disordered health to children, especially The grinders, which are evidently adapted if anything occurs to prevent the absorpto perform the operation which gives them tion and ready yielding of the gum to the their name, are found developed to the pressure of the tooth below. The absence fullest extent in animals which live wholly of teeth during the period of human inupon an herbaceous diet. Thus, all the fancy evidently indicates that the food recreatures belonging to the family of the quired at that period does not need their Ruminantia, which includes such well- employment. It is a well-known fact, that known animals as the sheep and the ox, the food of the infant is its mother's milk; the antelope and the deer, are not only but it is too often forgotten that, till teeth supplied with these teeth, but have them are developed, Nature does not intend the much more fully developed than the other child to take food that requires preparation teeth, which are, comparatively, of small by teeth in order to its digestion. The size, and in some cases absent. The pachy- practice of feeding young children with dermatous animals, to which the elephant, solid food, is the cause of great destruction rhinoceros, and hippopotamus belong, pos- of life, and even sops should only be sparsess also these teeth of a very large size. ingly administered, in cases of necessity, In all cases they are employed to break till the first teeth have appeared. down the coarser kinds of vegetable food From what we have before said, it will before it is finally passed into the stomach be seen that in the adult man there are for digestion.
thirty-two teeth, but if we examine the jaw The pointed teeth, or tearers, are found of a child after it has “cut all its teeth, most perfect in those families of animals and before it is six years old, we shall find which prey on other animals, and live on that it has but twenty teeth ; nor are these flesh. The most perfect exemplification of teeth increased in number by the addition the nature of these teeth is found in the of others; but, whilst this first set of teeth Carnivora, the order to which the lion and are performing their duties, an entirely new tiger belong. In these creatures the eye- set is growing underneath them, in precisely tooth and bicuspids are very large, and the same way as they did at first. Gradually their sharp points fully developed, and the fangs of the first set of teeth are abadapted to each other on opposite sides of sorbed in consequence of the pressure of the jaws, so as to serve at once as a powerful those beneath, and they fall out, or are means of holding as well as tearing up their easily removed, and make way for the others. living prey. The grinders in these animals The order in which the teeth appear—as are also more or less pointed on their sur- well as the time—is subject to considerable face.
deviations, but the following periods will The front teeth the incisors are be found to be about the time. adapted for gnawing and cutting, and we find these teeth especially prominent in
First, or Milk Teeth. the family of rodents, or Rodentia. This family includes the hare and the rabbit, the
2 lower middle incisors, 4th to 8th mnth. rat and the squirrel. They live chiefly on
ditto, 4th to 8th vegetable food, and this of a hard nature.
4 lateral incisors 7th to 11th Some of them even eat word; whilst such 4 anterior, or 1st molars, 12th to 18th as the squirrels procure their food by piercing
4 eye, or canine teeth, 16th to 22nd the hard coverings of the seeds of plants, as
4 back molars,
19th to 38th the various forms of nuts. Other families of animals have a mixture of these various 20 kinds of teeth, according to their food. In some children, the whole of the teeth
whilst, in others, the process of dentition rienced. It will also indicate how it is
that may be prolonged to the fifth year.
by the removal of a decayed part, and stop
ping it with some kind of cement, that Order of appearance of the permanent Teeth. access to the air is prevented, and the
danger of further decay removed. 4 first molars, one on each
Each hard part of the tooth is differently of the two sides of the
formed. The enamel is by far the hardest two jaws,
6th to 7th year. of these structures, and is composed of dense 4 middle incisors, two in
semi-transparent fibres placed side by side, each jaw.
7th to 8th year. and so small, that they do not measure more 4 lateral incisors, a little
than 3ooo part of an inch in diameter. later than the last, 7th to 8th year. These little fibres penetrate the dentine be4 first bicuspids,
8th to 9th year. neath. This substance is composed of two 4 last bicuspids, 10th to 12th year. parts, viz., a number of very minute tubes 4 eye, or canine teeth, 11th to 13th year. anastomosing with each other, and an inter4 second molars, 12th to 14th year. tubular tissue. The tubes commence in the 4 back molars, or wisdom
pulp-cavity, and pass on to the outside of teeth,
18th to 30th year. the tooth. The intertubular substance is
composed of very minute white granules or 32
globules. The cement which covers the The internal structure of the teeth is outside of the fang, has a structure prevery complicated, and has recently formed cisely like that of ordinary bone. the subject of very profound research These substances are not always disamongst the anatomists and physiologists tributed in the teeth of the lower animals of Europe. The minute structure is found as they are in man. In the gnawing anito be no less indicative of the species of mals, for instance, the enamel is only on animal to which it belongs, than the whole the front of the teeth, whilst the dentine is tooth itself; so that with regard to the exposed on the back of the tooth. The teeth we may say, that a morsel so small consequence of this arrangement is, that the as not to be distinguished with the naked dentine, wearing up much quicker than the eye, should yet enable the skilful anatomist enamel, the latter is always left with a to judge of the form of the whole tooth, sharp edge. Those who know the history and thence to infer the particular kind of of agricultural implements will recollect animal to which it belonged. We cannot that the very principle is involved here go into the details of the dental structure which has been so successfully applied to of the lower animals, but all that possess the making of ploughshares, by having one true teeth exhibit the same facts as we find side of soft iron and the other of steel, and in man, If we make a vertical section of which has led to the formation of one of a tooth (Fig. 7) with a fine saw, and, after the largest manufacturing establishments having polished it on a hard and smooth in the east of England. The same prinwhetstone, submit it to an examination ciple is acted on in the formation of the under the microscope, we shall easily make elephant's tooth, in which plates of enamel out the parts indicated in Fig. 7. We shall are inserted crosswise through the teeth, discover that there are three very distinct and these are separated by dentine and portions. First, the enamel (Fig. 7, a), cement. The more rapid wear of the denwhich covers the whole of the external part tine and cement keeps the enamel of the of the tooth; second, the dentine - tooth constantly projecting, and thus sethis substance, which is so largely deve- cures a roughened surface for the more loped in the tusks of the elephant and other effectual trituration of the coarse food of pachydermatous animals, constitutes ivory; these animals. third, the cement (c) or bone, forming the The teeth are inserted in, or rather, deexternal covering or facing of the tooth. veloped out of, the upper and lower jaws. In the middle of the tooth (d) is the pulp The upper jaw is fixed, but the lower jaw cavity. Into this cavity the nerves and has two round projections, which are inblood-vessels of the tooth penetrate, and serted into cavities in the skull, in which thus serve to maintain the living connexion they move with great facility. This movebetween the tooth and the rest of the body. ment is different in different animals. In The distribution of the nerve (e) in this those creatures which feed upon vegetable cavity (Fig. 6) will serve to explain how it fibre, as it exists in the leaves and branches is, that when any portion of the tooth 1 of plants, the jaw admits of a lateral motion,
and the trituration and reduction of this as that which is most desirable for his suskind of food is thus ensured. On the other tenance. hand, in animals which partake of food that Having said thus much with regard to requires no bruising before it is carried into the teeth, we conclude with a few directions the stomach, this lateral movement would as to their use, and the keeping them in be of no use; hence in the carnivora we find integrity. In the first place, then, it is evithis action of the jaw confined to a simple dent that the teeth of men are only adapted
for dividing and triturating flesh and vegetables; and the delicacy of their structure would seem to indicate that even these forms of food should be cooked. The teeth of man neither possess the sharpness and strength of those of the lion, nor the broad surface of those of the ox or the elephant. The attempt to masticate hard substances —to crack nuts, or in any other manner to strain the strength of the teeth and jawsis injurious; and many persons have to regret all their lives foolish practices of this kind.
In the next place, the teeth should be regular. The want of harmony between the upper and lower teeth is sometimes so great, that the food is only imperfectly masticated. In the lower animals, occasionally, one tooth is lost, when its opponent grows to a length that is injurious to the animal. This is especially the case in the rodents; and sometimes the teeth, from this cause, grow so long, as to penetrate the parts of the face beyond the jaw.
The irregularity of teeth produces an accumulation of tartar at their base, which causes an absorption of the gum, and even
tually the tooth drops out without decay. Fig. 7.
These irregularities arise from inattention
to the teeth during second dentition ; but up-and-down movement, by which the food if proper care is taken at that period, all is merely divided or cut into smaller pieces. undue growth may be guarded against. When we examine the jaw of the human The teeth should be kept clean. There being, we find that it has a combination of are two sources of impurity to the teeth. these two movements—that it combines the The first is from a deposit of tartar upon rotatory action of the ruminant with the them near the gum; and the second is from up-and-down movement of the carnivora. portions of food adhering to them after
In the course of our remarks we shall meals. The accumulation of tartar is a have to speak more particularly of the frequent source of disease in the teeth and nature of the food of man; but we would gums, and precautions should be taken to here point out, that in the structure of the prevent its adherence to them. The best jaws and teeth, we find a clear indication plan is that of cleaning them with the that he is adapted for taking food from both brush night and morning. Dentifrices are the vegetable and the animal kingdom, frequently employed, and, perhaps, when seeing that in the organs which prepare the simple, they are of service. All chemical food for digestion, we find instruments products, however, should be avoided. adapted for the preparation of both forms Anything which acts chemically upon the of diet. This is but one of many arguments tooth, will open the way to speedy decay. that may be brought against the advocates The simplest dentifrice, and one of the of an entire animal or vegetable diet; and best, is a mixture of prepared chalk and had we not such abundant proof in the well-powdered camphor. The chalk acts structure of man, we might appeal to his as a scouring material, whilst the camphor instincts, which, under all natural circum- stimulates the gums, and counteracts the stances, have dictated to him a mixed diet | decomposition of any small particles of food
that may lurk amongst the teeth. The —we do not speak at all, for it is not conpurer the water that is employed for wash- versation, but slow prattle; too tinctured ing the teeth the better.
with the germs of vice to be childish, but To cleanse away portions of food adhering too silly for the utterance of men. to the teeth, the toothpick should be used. speak of what bears the name of conversaMetallic toothpicks are objectionable. Those tion amongst the reading and thinking pormade of bone or quills are to be preferred. tion of middle-class society, which is to be
When teeth are found to be decayed, heard at social gatherings, at quiet dinner immediate attention should be paid to them. parties, and by the family tea-table. The They more frequently indicate serious de- | conversation in these quarters is not equal rangement of the health than is imagined. to the personages; they are apt to descend Where teeth are already decayed, they can below themselves for the sake of displaying not be restored to their pristine integrity; incipient wit, imperfect knowledge, execrabut the decayed part may be removed, or ble powers of criticism, or for the achievethe whole tooth ‘may be extracted. The ment of some petty conquest in argument. sooner this is done the better; for decay has Pity that many good societies should be an undoubted tendency to spread, and marred by unbridled and untamed tongues. nothing is so disagreeable to other people Pity that conversation is not everywhere as the breath of a person tainted with the made a matter of study,—that men will not faint odour of decomposing teeth.
exercise as much care in speaking their Decay of the teeth frequently comes on thoughts as they do in writing them. from long-continued indigestion, from ex- Among the most glaring social blunders posure to cold, from a scrofulous habit of to be noticed under this head are, talking body, from eating and drinking very hot too much of ourselves. This is a blunder or very cold articles of diet. Now, in all very commonly committed, and is as much diseases, prevention is better than cure. a inark of vanity as want of sense. Really Persons should take care to avoid those great men have never said much of themstates of the system, and those causes which selves; therefore we may infer, by the conare known to be favourable to the produc- verse argument, that he who indulges in tion of decayed teeth.
talking of himself must be a really small (To be continued.)
man. In the whole of Shakspeare's plays and poems you do not gather enough of the
poet's history to settle definitely the quesCONVERSATION.
tion whether he was lame or not, or even CONVERSATION ranks the high tamong to fix, with any certainty, his opinions on social enjoyments. To converse well re- political and religious subjects. He who quires extensive knowledge, elegance of talks much of himself is also apt to tell of manner, command of temper, and a desire the injuries he has sustained.
This is a to please. He who cannot converse to the very common blunder, but a most unparprofit of the company, must listen for the donable one. It is undignified to carry our profit of himself; though no one reed woes about with us, and retail them out to preserve a stolid silence from excessive others, saying how such-a-one has cheated us bashfulness or conscious inability. The of money, how another has offered us an smallest remark may be well-timed and ele- insult, and so on. If you cannot say somegantly uttered; the lightest observation thing cheerful to your friend, keep at a disproperly pointed and emphasised, and the tance, and let him enjoy at peace his own most trivial question put with modesty, cogitations. What are your affairs to other grace, and elegance of expression. Yet, in people ? keep your own counsel, and be not middle-class society, how little really good too ready to make confidants. conversation do we hear! How frequently If you are not to talk of yourself freely, personalities creep in; how one gives way so are you not to talk freely of others. to undue warmth when his religious and regret to have to confess here, that scandal, political principles are assailed; how another in some shape or other, is the bane of our jests and puns upon the most serious sub- English society, and needs as severe lashing jects; or a third plays the pedant by the use now-a-days as it did when Sheridan wrote of a string of technicalities, which he him- his wonderful comedy. Though when these self scarcely understands, to adorn his shal- poges meet the reader's eye he will perhaps low learning and his imperfect judgment. be unwilling to own it, but I will still Of that shallow talk in which the fast-going insist, that both seves are universally men of the day indulge-a drawling mix- addicted to this vice in some form or other; ture of the quasi-fashionable and the idiotic and that it is sheer vanity, or perhaps even
shame, which prompts men to make the , and trunkmakers. Those who sit in such a
names of Aquilegia Canadensis or AnagalContradictions are usually given too lis arvensis. Such terms are neither eleabruptly, and sometimes lead to wrang- gant nor appropriate in mixed society; and ling, or if not noticed by the parties so far from causing the ladies to look up in receiving them, are still apt to rankle and astonishment at the profound learning of annoy secretly, and destroy the harmony the speaker-an effect usually intended and which ought to prevail in an assembly of wished for-they are more likely to indulge friends. It is equally absurd' to make bets, in a sly titter, and vote him a bore. This or to strengthen a statement or argument is the "little learning" which Bacon terms by an offer of a bet in support Such a dangerous thing, and must be avoided tħings are worthy only of the lowest rabble, by those who would cultivate good breedand no man, making pretensions to the ing, which is always more allied to simplistatus of a gentleman, should descend to it. city of expression, and transparency of conOaths of all kinds are as ungentlemanly as duct, than to complicated technicalities, or they are wicked; and the frequent use of dark mysterious doings. Another fault of the condemnatory oath, as verb, adjective, Mr. Smallweed is, that he never pays proand noun, both immoral and degrading. per attention to another speaker; the music There are
some men, of respectable of his own voice is too great a charm for position and pretensions, who are so barren him, and he thinks it must have a sirenof general intelligence that they can talk of like tone to others; so he rambles on till nothing except their own business affairs. some wag asks him if he has a dictionary Such men
are very worthless in social with him, when he drops into sulkiness, society, and we conjure the reader at all looks black, and is quieted for a time. times to steer clear of conduct which so While upon Mr. Smallweed's failings, let readily indicates vulgarity and emptiness. me refer to his habitual mode of referring to A tradesman will perhaps sit down at your other persons, for this fault of his is very table, and endeavour to entertain you with common to the civilized specimen of (to use an account of sales and purchases; anon his phrase) the anthropological animal. For comes a thin-minded solicitor's clerk, who instance, instead of saying, “My friend, brings with him a string of appeals and Mr. Simpson, told me so-and-so,” he invamotions; then an incipient author, who riably says, "Simpson told me só-and-so." tells you of the immense mass of verses, he A few short rules for conversation may has written for the behoof of cheesemongers I here be useful; and I offer them in the