Section Iii. From _london Lancet_, July 25, 1903

EVILS RESULTING FROM INEFFICIENT MASTICATION

Too much food is eaten.--Inefficient mastication conduces to excessive eating. Now it is obvious that soft foods, and these constitute the bulk of our modern dietary, pass much more readily into the stomach than coarse, hard foods which compel a certain amount of preliminary mastication, and for this reason the former predispose to excessive eating: hence a danger at all periods of life, not only in grown-ups but in children, even infants; brought up as the latter are, mainly on liquid and pappy foods, many of them consume not only far more than is needful, but far more than is healthful, their stomachs being literally deluged with nutriment.

When the food is of a kind necessitating abundant mastication it is much less likely to be taken in excess, for the longer the time spent in mastication the less will the individual be tempted to consume; even in the case of soft food, less will probably be eaten if it be thoroughly masticated and insalivated than if it be bolted. Thorough mastication, however, not only tends to diminish the amount of food consumed on account of the time and labour which it entails; it actually reduces the amount needful to constitute a sufficiency, for the more perfectly the food is chewed the more perfectly is it digested and the more economically is it disposed of in the system; the less, moreover, is the tendency to that morbid craving for food which is so frequent an accompaniment of defective digestion. It is certain that appetite and the needs of the system are sooner satisfied when food is well masticated and digested than when it is swallowed whole.

A mass of unmasticated food may lodge in the throat and cause fatal suffocation.--This may seem to be a very exceptional kind of evil, but I am informed by one whose experience makes him an authority on the ways of the British soldier that it is by no means uncommon for soldiers in barracks to die from this cause. Usually it is when they are under the influence of alcohol that fatal results occur, post-mortem examination disclosing large undigested masses of food in the stomach. A like experience is also frequently met with in the case of men killed by accident.

The presence of masses of imperfectly masticated food in the stomach may cause disturbance either mechanically or by reason of their imperviousness to the gastric juices.--We have already seen that the digestibility of a food is largely determined by its consistence, and that many articles of diet, such as cheese, hard-boiled egg, cocoa-nut, lobster, and new bread, which have the reputation of being very indigestible, can, if finely comminuted by chewing or otherwise, be rendered quite digestible. Such articles are indigestible essentially by reason of their compactness; the compact lumps, but little pervious to the gastric juice, tend to undergo abnormal chemical change in the stomach, and may in this way cause violent local irritation, even to the extent of setting up acute gastritis; or they may paralyse the nerves of the stomach and check gastric secretion and movement, and thus remain in loco wholly undigested for hours or even days; or, again, more distant nervous effects may be produced, such as frontal headache, which may be felt almost immediately after ingestion of the peccant substance, being of reflex rather than toxic origin, and presumably in some cases, at least, due to the mere mechanical irritation of the stomach. The passage of imperfectly digested food into the bowel may still further aggravate matters. It does not seem improbable that the habitual bolting of food, by the prolonged local irritation to which it gives rise, may predispose to cancer of the stomach: Napoleon was a notorious fast eater and it is well known that he died from this disease.

While, however, the bolting of food readily sets up disturbance in some, it must be conceded that in many it seems to cause little or no inconvenience; especially is this the case in the young with vigorous muscular stomachs capable of triturating the food, and thus doing duty for the teeth. The human stomach is, indeed, a long-suffering organ, and wonderfully tolerant of ill-treatment, sometimes almost rivalling in its hardiness the gizzard of the bird. Nor is this surprising when we reflect that it is, in the ordinary course of nature, constantly exposed to the entrance of noxious substances. In this respect it stands in marked contrast to the intestines, for not only are highly irritant substances often vomited rather than passed onwards, but in ordinary circumstances the gastric contents are not allowed to pass the pylorus, until they have been duly prepared by the stomach; the pylorus, in fact, stands guard over the entrance to the bowel and is jealous of anything passing it which is likely to injure that canal.

And just as the pylorus protects the bowel so, in exceptional cases, may the œsophagus protect the stomach, regurgitating, after the fashion of the ruminants, insufficiently masticated bits of food, in order that they may be re-masticated. I have myself met with cases in point. Sometimes, in cases of this kind, the œsophagus may be dilated into a sort of proventriculus, which is capable of temporarily lodging a large quantity of food. Such a proventriculus is said to have developed in an apprentice who, not being allowed sufficient time for his dinner, rapidly bolted it, to regurgitate it after working hours and to chew the cud at leisure. Whether in these cases the food is ever returned from the stomach itself I am unable to say.

While the stomach is the organ especially liable to be injured by the swallowing of lumps of unmasticated food, the bowel may also suffer, especially the cæcum and vermiform appendix. And here we come to one of the most serious indictments against the bolting of food; though man has doubtless always suffered from appendicitis, there can be little doubt that this malady is more common now than it used to be; and there is equally little doubt, in my own mind at least, that the cause of its greater frequency is related to his food. I do not propose to discuss here in detail how food is capable of causing appendicitis, but will merely refer to one of the ways in which it may do so. I had already come to the conclusion that the habit of bolting food is a potent cause, when I read Sir Frederick Treves’s Cavendish Lecture in which he makes that contention. Sir Frederick Treves points out that in this rushing age people, especially business men, are apt to hurry over their meals and to take them at irregular times and often while standing at a bar; even when there is more leisure, food is rarely masticated nowadays in the same thorough way that it was in the old time, when it was of a coarser nature: hence solid lumps, especially in the case of such articles as pine-apple, preserved ginger, nuts, tough meat, and lobster, are apt to pass beyond the pylorus and, escaping intestinal digestion, to lodge in the cæcum and precipitate an attack of appendicitis, the most common predisposing cause of which is a loaded cæcum, often preceded by constipation. Sir Frederick Treves contends that this distended state of the cæcum encourages catarrh of the appendix by dragging upon it and blocking its orifice, as well as by twisting it and thus interfering with its blood-supply.

An excess of starch is apt to pass into the stomach.--We have just seen that inefficient mastication tends to promote over-eating, and what has been said on this head applies to all kinds of food, starchy foods among others. It leads, however, to a further evil as regards these latter; not only does it tend unduly to increase the quantity of them consumed, but it too often causes the stomach and intestines to become flooded with starch in a wholly undigested form. I cannot too frequently repeat that in ancient times, especially in the pre-cooking age, laborious mastication was needed in the case of all starchy foods, partly because they were coarse and fibrous, but chiefly because the starch and other nutritive ingredients had, in order to become available for nutrition, to be liberated from their undigestible cellulose envelopes. In these days of prepared, soft, starchy foods, however, mastication is very little required for these purposes, but in other respects it is as needful as ever, indeed more needful, if the large quantities of starch which are now consumed are to be insalivated effectually. The laborious and sustained mastication to which primitive man was compelled to subject his limited supplies of uncooked starchy food, went far to effect complete digestion of the starch within the mouth, for raw starch is freely digested by the saliva, and hence in his case very little passed into the stomach in a wholly undigested form. How different is the case with us moderns. Since the opening of the era of agriculture and cooking, man has enormously multiplied his supplies of saccharide, and he now consumes large quantities of starch which has been freed from its cellulose framework by cooking, milling, grinding, and the like, and reduced to a soft or pappy form, such as milk puddings, porridge, boiled potatoes, and new bread, all of which can be swallowed with little or no preliminary chewing; and when food can be swallowed easily, without mastication, few will take the trouble to masticate it. In these circumstances the starch does not undergo adequate salivary digestion, and a large quantity passes wholly undigested into, and out of, the stomach, not beginning to be digested until it reaches the bowel. Small wonder that the latter should rebel again this invasion and that flatulence, pain, and other dyspeptic evils should result.

It is especially in young children that these evils are observed. Too often the stomach of the child, semi-carnivorous, remember, by its ancestry, is literally deluged with pure starch. At the seventh or eighth month, or even earlier, for many of the patent infant foods contain it, this substance is poured into the stomach without being afforded any opportunity of undergoing salivary digestion; and for a long time after infancy large quantities are given in the liquid or pultaceous form, such as rusks soaked in milk, puddings, and mashed potatoes. This practice of deluging the digestive organs with starch, besides leading to the more immediate troubles connected with flatulent dyspepsia, gives rise to abundant formation of toxins which, by irritating the alimentary mucous membrane, set up gastro-intestinal catarrh; this, again, intensifies the dyspepsia already existing and causes a still further production of toxins, so that the motions become intensely fœtid. These poisons being absorbed into the blood the tissues become saturated with them and the nutrition of the entire organism is disturbed, the faulty metabolism manifesting itself by a diminished resistance to pathogenic agencies, by a tendency on the part of the tissues to inflame (as shown by a liability in children thus fed to bronchitis, rhinitis, naso-pharyngitis, and tonsillitis), by their proneness to tuberculosis, and finally by a disposition to rickets, which I little doubt is essentially of toxæmic origin.

Besides the above-mentioned troubles an excess of starch in the stomach may set up hyperchlorhydria--i. e., that form of dyspepsia in which there is excessive secretion of hydrochloric acid. This affection occurs during the most vigorous years of life and is apparently due to excessive activity on the part of the gastric glands. The excess of acid does not give rise to any symptoms so long as there is any unsatisfied proteid in the stomach to unite with it, but directly all the proteid is satisfied and free acid is present in the stomach, pain, heartburn, and distention are apt to be felt; hence these symptoms are generally removed temporarily by a meal, the food ingested seizing upon the free acid, and tend to recur in the course of an hour or two. Other symptoms are mental and bodily lassitude and great mental depression, while, if the condition is long-continued, gastric catarrh and dilatation ensue. Eructation of the acrid mass, its removal with a tube, or its dilution or neutralisation by an alkali, causes relief of the symptoms. Now Dr. William Russell, who has recently studied this form of dyspepsia, has shown, and the fact is most significant from our present point of view, that in it starch is the last constituent to leave the stomach; that when this organ has so far emptied itself as to contain but one or two ounces of very acrid material the residue consists chiefly of finely divided undigested starch, which continues to stimulate the gastric secretion; “and, there being no more proteid with which to combine, the secretion accumulates and leads to hyperacidity.” Inasmuch, then, as inefficient mastication leads to an excess of starch in the stomach, we see how it may predispose to hyperchlorhydria and we shall presently see that there is yet another reason why it should do so.

It will be gathered from the foregoing that thorough mastication is the most effective way of securing efficient starch digestion. This simple fact has been most strangely overlooked. Thus “van Valzah considers that not a little of the difficulty of the digestion of starches and cereals can be overcome by more thorough cooking. Patients who cannot eat potatoes after ordinary cooking are [he urges] often able to digest them very readily if they are doubly cooked before being served. Cereals, as a rule, should [he contends] be allowed to simmer all night and then be thoroughly cooked for a half hour in the morning before being eaten.” This is an admirable illustration of the modern tendency to cheat the mouth of its proper work. A much more rational way of facilitating starch digestion in those who experience a difficulty in this respect is by efficient mastication.

Evils resulting from an insufficient quantity of alkali in the stomach.--I doubt if it is adequately realised what a large amount of alkaline saliva passes into the stomach as the result of prolonged mastication. Its presence there serves the useful purpose of prolonging the period of starch digestion within the stomach, while it further aids gastric digestion not only by exciting the secretion of gastric juice, but also by its influence on the reaction of the gastric contents; it can scarcely be doubted that the effect is on the whole one favourable to digestion in general. We have just seen that defective mastication may predispose to hyperchlorhydria by allowing an excess of pure starch to pass into the stomach, and I suggest that it may further operate in the same direction by cheating the stomach of its due supply of alkaline saliva. Now the saliva in this affection is apt, as was pointed out by Sir William Roberts, to be superalkaline, and for this reason he recommended his acid-dyspeptics to excite the flow of it by chewing gum-mastic with the object of neutralising the gastric hyperacidity. That relief can thus be obtained there can be no doubt; but it is surely more rational to get the patient to stimulate his salivary glands by masticating actual food, by which we secure the additional advantages accruing from its complete insalivation and comminution as well as from the reflex gastric effects. Actuated by these considerations, I have long been in the habit of recommending hyperchlorhydriacs to subject their food to prolonged mastication, this being, in my belief, the most rational and effective way of breaking the stomach of its vicious habit. In extreme cases we must insist that each morsel of food should be chewed at least one hundred times and not permit any relaxation of this severe discipline, until the stomach has been schooled into healthier ways. Evils in connection with the jaws and their appendages and the adjacent structures: the nasal passages, naso-pharynx, and faucial tonsils.--In those who do not masticate properly in early life these parts fail to develop as they should, and they are on this account alone predisposed to disease; their resistance to disease is still further lowered by the fact of their blood and lymph flow not being adequately stimulated by the vigorous exercise of the masticatory muscles. Now we have seen that the great cause of defective mastication in children is the softness of the food given them and that the feeding of them upon an excess of soft food, especially the starchy kind, disturbs digestion, induces toxæmia, and in this way evokes a catarrhal tendency. In children thus fed we have therefore several conditions which make for disease in the parts under consideration--defective development, sluggish circulation, and toxic saturation. Is it any wonder that the modern child should be liable to disease in these regions, that he should so frequently suffer from rhinitis, naso-pharyngitis, tonsillitis, and from hypertrophy of the pharyngeal tonsil (“adenoids”) and of the faucial tonsils?

It is in this way that I would explain the frequency of adenoids among the children of civilised communities. I claim, in fact, that this disease is largely dietetic in origin. I submit that a child whose nasal apparatus and naso-pharynx are well-grown and habitually bathed by a stream of pure blood and lymph, periodically accelerated by an ample and vigorous use of the masticatory muscles, is unlikely to contract adenoids. On the other hand, I contend that a child in whom these parts are ill-developed and bathed by an habitually sluggish stream of tainted blood and lymph--one, i. e., that is not only poisoned, but rarely, if ever, hurried along its lazy course by due exercise of the muscles of mastication--I submit that such a child runs great risk of contracting the disease. The influence in setting up adenoids of toxic saturation with its resulting catarrhal tendency is shown by the frequency with which this affection follows upon the rhinitis and naso-pharyngitis of measles and diphtheria, and in order to realise how greatly the circulation of blood and lymph in the walls of the naso-pharynx must be influenced by mastication, one has but to remember how very closely the pterygoids are related to this region; in exploring it for adenoids they can, indeed, often be felt to stand out prominently.

This, then, is my explanation of the truly fearful prevalence of adenoids among the moderns. It is essentially a disease of pap-fed peoples. A child may, with the one exception that he is fed on a pappy, super-saccharide diet, be brought up under ideal health conditions. He may live in the heart of a dry, open country, far from the darkness, dust, and tainted atmosphere of the town, sleep with the windows open all night, live out of doors all day, be fed on the most nourishing (too nourishing, it may be) food, be clothed after the most approved methods, and yet, in spite of all this, we may find his naso-pharynx packed with adenoids. This disease is, in fact, scarcely less prevalent in the country than in the towns, scarcely less common among the rich than among the poor. Yet in primitive communities it is practically unknown. And what, I would ask, is the one condition in the material environment of my supposititious child differing from that of the primitive child? What but the factor of diet? Therefore, I say, the prevalence of adenoids among moderns must be the result of the modern system of feeding children, and the defective mastication which goes along with it.

That the foregoing is a grave indictment against that system, it need scarcely be said. For adenoid disease is fraught with many evils, among them mental hebetude, blocking of the Eustachian tubes, and manifold other auditory troubles, gastro-intestinal disturbances from the passage into the stomach of unhealthy discharges, and, most serious of all, nasal obstruction and consequent mouth-breathing. So serious are the evils connected with this latter habit that they demand more than a passing reference. Pronounced adenoid disease is always associated with mouth-breathing, and there can be no doubt that in the majority of these cases, the nasal obstruction is not in the nasal passages primarily, but is due to a blockage of the posterior nares by the adenoid growths, for it generally happens that nasal breathing is rapidly re-established after their removal, though in a certain proportion of cases the obstruction still persists, and has to be dealt with by treatment directed to the nasal passages themselves. Some have, indeed, contended that a primary nasal obstruction is one important factor in the induction of adenoids, leading as it does to a dry-cupping of the naso-pharynx during inspiration and to a consequent congestion of its lining membrane. I am quite ready to allow that this mechanism may play some part in causation, and such an assumption is in entire harmony with my main contention that adenoid disease is of dietetic origin, for nasal obstruction in children, other than that caused by adenoids, is mainly due to defective development of the nasal passages coupled with inflammation of their lining membrane, both of which conditions may, as we have seen, be essentially the outcome of defective diet.

Coming now to the evils resulting from mouth-breathing, we have first to remember that normally the air is inhaled through the nose, and is thus warmed, moistened, and filtered before being allowed to pass into the lungs; but in the mouth-breather the air, which may be dry, cold, and dust-laden, passes at once unprepared through the mouth into the lungs, impinging in its passage against the pharynx, thus drying and mechanically irritating the mouth, pharynx, larynx, and bronchial tubes, all of which are thereby predisposed to disease. In this way laryngitis and bronchitis, nay, even phthisis, may be induced. Dental caries is also predisposed to by the habit of breathing through the mouth. Mouth-breathing further interferes with the proper development of the cranial bones, but especially of the maxilla, giving rise to what may be termed the “mouth-breather’s jaw,” so characteristic is it I do not propose to discuss here the mechanism by which this deformity is produced, interesting though the question is; suffice it to say that nasal breathing is essential to the normal development of the jaws. The deformity in question, though it involves the maxilla chiefly, affects also the mandible from the fact of its being, to a large extent, moulded on the maxilla; in typical cases the maxilla is small and its alveolar ridge does not attain its normal length, but is compressed laterally towards the sagittal plane, giving rise to the false appearance of a “high arch” and often thrusting the anterior portion of the ridge forwards; the teeth, the growth of which is not so much interfered with as that of the imbedding bone, are thus prevented from taking up their proper positions and show irregularity, sometimes extreme. Dental irregularity may also, as we shall see, result from inadequate use of the jaws in mastication, but not to the extent which is frequently observed in the mouth-breather’s jaws, and therefore pronounced dental irregularity always shows that there has been protracted nasal obstruction, and this in the vast majority of cases implies the existence of adenoids, past or present; I say in the “vast majority,” for in a few rare cases long-continued nasal obstruction in children originates primarily in the nose and may lead to the typical mouth-breather’s jaw, with the resulting dental irregularity.

The tongue.--If the tongue is not properly exercised in childhood and youth, we find it imperfectly developed; hence in inefficient masticators it is generally small. It must not be forgotten in this connection that this organ is considerably exercised when the infant is at the breast, from which the milk is obtained, not by suction, but by a vigorous tugging and squeezing of the nipple (in which the tongue takes considerable part), whereby the gland is reflexly excited to secrete. When, on the other hand, the child feeds at the bottle he obtains his milk by actual suction, and generally through an orifice of such ample dimensions as to allow the bottle to be rapidly emptied with comparatively little exercise of the lips and tongue. In short, the breast-fed infant has to do some work for his living, and that of a sort calculated to promote the health of the jaws and their appendages, while the bottle-fed child can glut himself by doing very little more than opening his mouth; wherefore we find the tongue and adjacent parts less developed in the latter than in the former. It may be thought to be a matter of indifference whether the tongue develops to its normal proportions or remains small, but such is by no means the case, for, as Dr. J. Sim Wallace has shown, the pressure of this structure against the teeth promotes the normal development of the jaws, especially of the mandible, and when it is small they are apt to be so too.

The salivary glands.--Just as mastication increases the functional activity of the salivary glands and buccal glands and favours their normal development, so, contrariwise, inefficient mastication during early life fails to call forth their normal functional activity and to secure their adequate development. Thus we find that a child who has been brought up on hard, starchy foods, necessitating abundant mastication has much larger and more active salivary glands than one who has been fed on soft foods which slip down into the stomach before they have had the chance of being properly masticated, and it is needless to say that the more efficient these glands are the more likely is digestion to be carried out satisfactorily.

The jaw-bones.--If the jaws are not adequately exercised in youth by mastication they fail to grow to their normal size and shape, and there is apt in consequence to be overcrowding of the teeth. The main defect of the jaws in such cases is their smallness; they do not present that pronounced lateral compression and anterior protrusion which characterise the mouth-breather’s jaw, nor such extreme dental irregularity, the most common being overlapping of the incisors, displacement of the canines, and difficulties in regard to the eruption of the wisdom teeth from shortness of the alveolar ridge. I have already referred to the progressive shortening in the post-molar ridge, which has been taking place during man’s evolution from the anthropoid in correspondence with the alteration in his diet.

We thus see that defective use of the jaws leads to irregularity of the teeth (1) directly and (2) indirectly through the induction of adenoids. This irregularity is not only unsightly but leads to certain evils which thus primarily owe their origin, in large measure at least, to defective mastication. What, then, are these evils? In the first place, dental irregularity predisposes to dental caries by favouring the lodgement of food between the teeth; in the next place, it leads to defective “bite.” Now when the bite is defective adequate mastication is impossible, for not only is it impossible in these circumstances to oppose the teeth properly, but also, owing to their interlocking, to accomplish that free lateral movement of the lower teeth against the upper, which belongs to normal mastication. I do not say that defective bite is the sole cause of this imperfect lateral movement; it may, indeed, be observed in most moderns brought up on soft pappy food, whether the bite be good or not. Normal mastication is, in fact, becoming a lost art; the average modern masticates mainly by a vertical compression of the lower teeth against the upper, and in only a small degree by a lateral frictional movement which, it is needless to say, is the more effective method for grinding purposes; and it is, I doubt not, chiefly for this reason that the teeth of modern man are so much less worn down than those of primitive peoples.

The teeth.--Imperfect use of the teeth leads to many ills. When adequately exercised and made to execute for one or two hours every day a lively dance in their sockets, during which the circulation of blood and lymph in the tooth-pulp, periodontal membrane, and surrounding tissue of the gum is vigorously stimulated, and the cavity of the mouth is bathed in a copious flow of salivary and other buccal secretions, we have conditions which make alike for the health of the buccal mucous membrane, of the teeth, and of the periodontal membrane and alveoli; but when the circulation is not duly stimulated in this way the teeth do not develop properly, while the secretions of the mouth are apt to be scanty and unhealthy, both of which conditions predispose to caries. How far dental caries is due to inherent dental weakness and how far to faulty conditions outside the teeth we need not stop to inquire; Dr. Wallace attributes little influence to the former factor, contending that caries depends essentially upon faulty dental environment; and one can scarcely doubt that the state of the gums and of the oral secretions profoundly influences the growth of bacteria in the mouth, upon the acid yielded by which organisms the corrosion of the dental enamel essentially depends. Faulty conditions of the oral secretions likewise favour the deposit of tartar.

Another result of imperfect use of the teeth is undue thinness of the alveolar walls and periodontal membrane, in consequence of which the teeth are not so firmly held in their sockets as they should be. This is, I believe, one of the reasons why they are prone to fall out prematurely among the moderns: we know that the teeth tend to drop out in old people owing to a senile atrophy of the alveolar walls; the Haversian canals get smaller and may, indeed, disappear entirely, and it stands to reason that this atrophy must be hastened by inefficient exercise of the teeth. So far as I am able to gather from an examination of skulls in museums, the teeth are rarely shed among primitive peoples before extreme old age, while among moderns they frequently fall out long ere this is attained.

A still worse evil attaching to insufficient use of the teeth is pyorrhœa alveolaris or Riggs’s disease, which, in conjunction with the deposit of tartar, is the great cause of the premature loosening and shedding of the teeth observed among latter-day civilised peoples. This affection consists of a purulent inflammation of the periodontal membrane, owing to the invasion of it by pyogenic cocci, so that pus wells up on pressing the gum against the teeth. Now, when by a vigorous use of the teeth the buccal cavity is kept well flushed with healthy secretions, the growth of micro-organisms within this chamber is kept down, and when, by the same means, the vitality of the periodontal membrane and adjacent tissues of the gum is periodically stimulated, these tissues offer stout resistance to the invasion of pathogenic organisms; but when, contrariwise, the teeth are little used, the secretions of the mouth are in consequence defective both as to quality and quantity, and the growth of organisms in the buccal cavity is promoted; and when, further, the circulation in the periodontal membrane and adjacent soft tissues is not adequately stimulated by vigorous mastication, their vitality is poor and they offer but a feeble resistance to parasitic invasion. We can thus, I think, safely infer that inefficient mastication is a potent cause of pyorrhœa alveolaris; and the chief cause of inefficient mastication being the eating of soft foods, we must also conclude that the latter practice is chiefly responsible for the disease in question; such foods further predispose to this affection in that they are apt to lodge between the teeth and by undergoing decomposition there to favour the growth of micro-organisms within the mouth. The condition of the teeth and gums among the civilised poor is, alas, little calculated to make us proud of our boasted civilisation--the spongy pus-exuding gums, the lengthening, loose, tartar-covered, carious teeth, and the putrescent breath constitute a damning indictment against our modern system of living on a soft, pappy diet, and not giving the teeth the work for which they are designed. I never examine such a mouth without being impressed with, and I may add oppressed by, this fact.

I am not, of course, contending that pyorrhœa alveolaris only occurs in those who masticate inefficiently; whatever causes an unhealthy condition of the gums and saliva predisposes to it, but it is surely much less common in those who masticate well than in those who masticate ill. Confirmatory of this statement is the fact that it is more frequent in those with irregular teeth than in those with a good bite, who are thus able to put their teeth to more effective use. This affection is very common among the carnivora of menageries as well as among dogs and cats; indeed, one seldom fails to find it in dogs over four years of age, and in old dogs it is generally rampant. Doubtless in all these cases the general conditions of life play some part in the causation of the disease, but I do not think that we can eliminate from it the factor of defective use of the jaws and teeth, for it is certain that dogs and cats are fed largely on pappy foods and are often insufficiently supplied with bones.

The causation of dental caries.--Dr. Wallace, in his philosophical work on “The Cause and Prevention of Decay in Teeth,” contends that the cause of the prevalence of dental caries is that the natural food-stuffs are, to a large extent, ridded of their accompanying fibrous parts and consumed in a form which renders them liable to lodge and to undergo acid fermentation in the mouth; while from the same cause and the induced conditions the micro-organisms of the mouth lodge and multiply and augment the rapidity and intensity of the acid fermentation. I am perfectly at one with Dr. Wallace in believing that the removal of the fibrous portions of food is the main cause of the prevalence of caries among moderns, and I can hardly doubt that foods so prepared tend to promote caries in the way indicated, but I venture to think that they do this even more by failing to call forth the normal degree of mastication. I cannot but think that if these same soft foods were as laboriously masticated as they would need to be if they retained their fibrous ingredients, dental caries would be much less common than it actually is. I have endeavoured to show how very different the local conditions are in the efficient from what they are in the inefficient masticator--how in the former the jaws and teeth are wont to be well developed, the bite to be good, and the secretions which bathe the teeth to be of a kind calculated to promote their health; and how in the latter an entirely opposite set of conditions is wont to prevail. That it is possible to maintain a fine set of healthy teeth till past middle life on ordinary civilised diet, provided the food be habitually subjected to efficient mastication, is shown in the case of the man already referred to, and by numerous other cases which I have observed.

Since the application of cooking to food there has been a progressive lessening in the work of the jaws and teeth and, parallel with this, a diminution in their size and an incursion of dental caries. Among the anthropoids in their natural state caries is practically unknown, and I think we may conclude that the same was true of man before he learnt to cook. In the pre-agricultural races, such as the aboriginal Australians, the effect of cooking the food is shown in the lessening in the size of the wisdom teeth and of the post-wisdom alveolar ridge; dental caries, though rare among these people, does occur, and especially in the wisdom teeth. In the early agricultural period, owing to the increasing softness of the vegetable food, the jaws and teeth show a tendency to be smaller than in the previous periods; the wisdom teeth are decidedly smaller and more prone to caries, while caries of the other teeth is by no means rare. In the late agricultural period the jaws and teeth often show very decided defects of development, while dental caries is, as we know but too well, rampant.

What has been said concerning the relative prevalence of caries in different diet epochs applies to many other diseases of the teeth; thus, along with the increase of caries, there has been a parallel increase in the prevalence of pyorrhœa alveolaris.

CONCLUDING REMARKS

I have now set forth some of the evils resulting from inefficient mastication. They are many and serious. The immediate evils, such as over-eating, indigestion, adenoids, dental caries, and pyorrhœa alveolaris, are bad enough, but when we consider the secondary evils to which these primary ones give rise,--and I have only mentioned a few of them,--we must come to the conclusion that an appalling amount of misery and suffering may be saved by the simple expedient of inculcating the habit of efficient mastication. How this end can best be accomplished will be considered in the next section.