1
408 end ; but in a relatively long absence of preventive measures it showed no tendency to a violent flare-up or even to a slow serious extension. This is a phenomenon that has been previously observed- for instance, in Melbourne-and is clearly of epidemio- losdcal imnortancc. THE INNERVATION OF DENTINE FOR many years the destination of the abundant nerve-supply of the dental pulp has interested workers in dental histology. The extreme sensitiveness of dentine-so obvious both to dentists and their patients-made it seem likely that dentine possesses a nerve-supply. But the proof or otherwise of this by histological methods was far from easy, owing to the technical difficulties of preparing sections of hard and soft tissues in their normal relations. The late Howard Mummery, a histologist of unsurpassed technique, after many years’ patient.work, claimed to have shown that nerve-fibres entered the dentinal tubules. In a later paper he described a layer of nerve- cells, just below the odontoblast layer, round which the nerves entering the pulp aborised ; from these cells axons passed into the dentine and could be traced nearly up to the enamel. But this work, though it seemed to have solved the problem, has not passed unchallenged, and while some at least of Mummery’s conclusions may be true, the general problem is still unsettled. D. Stewart 2 approached it from another angle. He severed the inferior dental nerve in a cat on one side and later compared the pulps of the teeth with those of the opposite side. He found that histologically the fibres which Mummery had assumed to be nerve-fibres showed no difference in their staining reactions from those on the normal side ; he concluded that if they were nerve-fibres some change would be visible and that they must therefore be connective tissue fibres. But this work, significant though it be, does not take into account the possibility of some nerve-supply through the sympathetic fibres accompanying the blood-vessels. Another possible fallacy is that little is known of the changes in the staining reactions of non-medullated nerve-fibres after section of the parent axon, and an absence of any demonstrable change in fibres passing into the dentine might not necessarily mean that they were connective tissue fibres and not nerves. The latest contribution to the subject has been made by 0. W. Tiegs 3 of Melbourne. Using the Bielschowsky method, he has examined the pulps of young molar teeth, and finds that from the deeper layers of the pulp nerves can be followed through the odontoblast layer into the sub- dentinal zone. These fibres pass as fine filaments under the dentine and often run for a considerable distance among the odontoblast processes, on which they terminate in definite end-organs attached to their surface. Nerve filaments may also end by minute swellings on the odontoblast cells. Tiegs was unable to find any evidence of the existence of nerve- cells in the pulp as described by Mummery, nor could he trace the fibres into the dentinal tubes. He con- cludes that the odontoblast cells must act as receptor organs for the nerve-endings, and that it is unnecessary to infer a special innervation of the dentine when the histological findings do not support it. It is to be noted that the odontoblast cells which according to Tiegs act as receptors of painful impulses, are mesodermal and not epiblastic. But on this point he remarks that there is no a priori reason why sense organs should be 1 Microscopic Anatomy of the Teeth, London, 2nd ed., 1924. 2 Jour. of Anat., 1927, lxi., 439. 3 Ibid., 1932, lxvi., 622. exclusively epiblastic ; they are predominantly so because this layer is most likely to come into contact with the outer world. The careful character of this piece of work and the excellent illustrations which accompany it make it an important contribution to an interesting though slightly academic subject. In the absence of any confirmation by other workers of Mummery’s layer of nerve-cells in the pulp, this portion of his findings looks as though it must be abandoned as untenable. An examination of Mummery’s original sections, now in the museum of the Royal College of Surgeons of England, leaves no doubt that whatever their nature the fibres which he demonstrated as passing into the dentinal tubes are not artefacts ; though whether they are nerve-fibres as he assumed or whether they are connective tissue fibres remains uncertain. THE ÆTIOLOGY OF GOITRE Colonel R. McCarrison’s report to the Berne congress of 1927 summarised the knowledge of the aetiology of goitre at that time, but left many gaps to be filled. " The Life Line of the Thyroid Gland " * is a further memoir, written in association with Prof. K. B. Madhava, of Madras, which describes work done by the senior author during the past five years. Before further progress could be made in analysis of the factors which tend to produce goitre it was necessary, he says, to answer the question, What is the normal The material of research was a stock of albino rats, living under such healthy con- ditions in the laboratory that for three years there had been no illness or death from natural causes. The thyroid gland was removed from large numbers of animals of this stock and was weighed, glands being taken from both sexes at different seasons of the year, some from those living a normal life and others from those sexually isolated. The figures thus obtained served as controls for further observations. Similar investigations were also made in pigeons, guinea-pigs, and rabbits, and this mass of accumulated data, together with previous observations on man and animals, was subjected to statistical study by Prof. Madhava and forms the basis of the present memoir. The conclusions reached are of no little interest. In early life, it is found, the normal thyroid gland grows more rapidly than the body as a whole, and it is then that it specially needs all the elements necessary for normal nutrition. The maximum weight of the thyroid relative to the body is attained just before puberty, and thereafter it gradually falls in both sexes, though in females there are secondary rises associated with reproduction. It is noteworthy that these results obtained in animals are in agreement , with those of Percy Stocks for children, and that this normal enlargement of the thyroid gland at puberty is often mistaken for goitre in surveys of school- children. Of the influences which lead to goitre the , memoir especially emphasises faulty diet. According , to Colonel McCarrison a diet may be goitrogenic . because it contains excess of certain substances normally present, such as fats, fatty acids, and lime ; B because it is deficient in certain substances such as vitamins A and C, or iodine, or has a relative deficiency : of phosphates to lime ; or, lastly, because it contains L certain positive goitre-producing substances which are present in cabbage, ground-nut, bran, and maize, and possibly in certain other cereals. Lack of vitamin B 4 Indian Med. Research Mem., No. 23, 1932. Published for the Indian Research Fund Association, by Thacker, Spink and Co., Ltd., Calcutta. Pp. 378. Rs. 12/12 (19s.).

THE INNERVATION OF DENTINE

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408

end ; but in a relatively long absence of preventivemeasures it showed no tendency to a violent flare-upor even to a slow serious extension. This is a

phenomenon that has been previously observed-for instance, in Melbourne-and is clearly of epidemio-losdcal imnortancc.

THE INNERVATION OF DENTINE

FOR many years the destination of the abundantnerve-supply of the dental pulp has interested workersin dental histology. The extreme sensitiveness ofdentine-so obvious both to dentists and theirpatients-made it seem likely that dentine possessesa nerve-supply. But the proof or otherwise of thisby histological methods was far from easy, owing tothe technical difficulties of preparing sections of hardand soft tissues in their normal relations. The lateHoward Mummery, a histologist of unsurpassedtechnique, after many years’ patient.work, claimed tohave shown that nerve-fibres entered the dentinaltubules. In a later paper he described a layer of nerve-cells, just below the odontoblast layer, round whichthe nerves entering the pulp aborised ; from thesecells axons passed into the dentine and could betraced nearly up to the enamel. But this work,though it seemed to have solved the problem, has notpassed unchallenged, and while some at least ofMummery’s conclusions may be true, the generalproblem is still unsettled. D. Stewart 2 approachedit from another angle. He severed the inferior dentalnerve in a cat on one side and later compared the pulpsof the teeth with those of the opposite side. He foundthat histologically the fibres which Mummery hadassumed to be nerve-fibres showed no difference intheir staining reactions from those on the normal side ;he concluded that if they were nerve-fibres some

change would be visible and that they must thereforebe connective tissue fibres. But this work, significantthough it be, does not take into account the possibilityof some nerve-supply through the sympathetic fibresaccompanying the blood-vessels. Another possiblefallacy is that little is known of the changes in thestaining reactions of non-medullated nerve-fibres aftersection of the parent axon, and an absence of anydemonstrable change in fibres passing into the dentinemight not necessarily mean that they were connective ’

tissue fibres and not nerves. The latest contributionto the subject has been made by 0. W. Tiegs 3 ofMelbourne. Using the Bielschowsky method, he hasexamined the pulps of young molar teeth, and findsthat from the deeper layers of the pulp nerves can befollowed through the odontoblast layer into the sub-dentinal zone. These fibres pass as fine filamentsunder the dentine and often run for a considerabledistance among the odontoblast processes, on whichthey terminate in definite end-organs attached totheir surface. Nerve filaments may also end byminute swellings on the odontoblast cells. Tiegs wasunable to find any evidence of the existence of nerve-cells in the pulp as described by Mummery, nor couldhe trace the fibres into the dentinal tubes. He con-cludes that the odontoblast cells must act as receptororgans for the nerve-endings, and that it is unnecessaryto infer a special innervation of the dentine when thehistological findings do not support it. It is to be notedthat the odontoblast cells which according to Tiegsact as receptors of painful impulses, are mesodermaland not epiblastic. But on this point he remarks thatthere is no a priori reason why sense organs should be

1 Microscopic Anatomy of the Teeth, London, 2nd ed., 1924.2 Jour. of Anat., 1927, lxi., 439.

3 Ibid., 1932, lxvi., 622.

exclusively epiblastic ; they are predominantly so

because this layer is most likely to come into contactwith the outer world.The careful character of this piece of work and the

excellent illustrations which accompany it make itan important contribution to an interesting thoughslightly academic subject. In the absence of anyconfirmation by other workers of Mummery’s layerof nerve-cells in the pulp, this portion of his findingslooks as though it must be abandoned as untenable.An examination of Mummery’s original sections, nowin the museum of the Royal College of Surgeons ofEngland, leaves no doubt that whatever their naturethe fibres which he demonstrated as passing into thedentinal tubes are not artefacts ; though whetherthey are nerve-fibres as he assumed or whether theyare connective tissue fibres remains uncertain.

THE ÆTIOLOGY OF GOITRE

Colonel R. McCarrison’s report to the Bernecongress of 1927 summarised the knowledge of theaetiology of goitre at that time, but left many gapsto be filled. " The Life Line of the Thyroid Gland " *is a further memoir, written in association withProf. K. B. Madhava, of Madras, which describeswork done by the senior author during the past fiveyears. Before further progress could be made inanalysis of the factors which tend to produce goitreit was necessary, he says, to answer the question,What is the normal The material of research was astock of albino rats, living under such healthy con-ditions in the laboratory that for three years therehad been no illness or death from natural causes.The thyroid gland was removed from large numbersof animals of this stock and was weighed, glandsbeing taken from both sexes at different seasons ofthe year, some from those living a normal life andothers from those sexually isolated. The figures thusobtained served as controls for further observations.Similar investigations were also made in pigeons,guinea-pigs, and rabbits, and this mass of accumulateddata, together with previous observations on manand animals, was subjected to statistical study byProf. Madhava and forms the basis of the presentmemoir. The conclusions reached are of no littleinterest. In early life, it is found, the normal thyroidgland grows more rapidly than the body as a whole,and it is then that it specially needs all the elementsnecessary for normal nutrition. The maximum

weight of the thyroid relative to the body is attainedjust before puberty, and thereafter it gradually fallsin both sexes, though in females there are secondaryrises associated with reproduction. It is noteworthythat these results obtained in animals are in agreement

,

with those of Percy Stocks for children, and that thisnormal enlargement of the thyroid gland at pubertyis often mistaken for goitre in surveys of school-children. Of the influences which lead to goitre the

, memoir especially emphasises faulty diet. According,

to Colonel McCarrison a diet may be goitrogenic.

because it contains excess of certain substancesnormally present, such as fats, fatty acids, and lime ;

B because it is deficient in certain substances such as0 vitamins A and C, or iodine, or has a relative deficiency: of phosphates to lime ; or, lastly, because it containsL certain positive goitre-producing substances which’

are present in cabbage, ground-nut, bran, and maize,’ and possibly in certain other cereals. Lack of vitamin B

4 Indian Med. Research Mem., No. 23, 1932. Published forthe Indian Research Fund Association, by Thacker, Spink andCo., Ltd., Calcutta. Pp. 378. Rs. 12/12 (19s.).