ambition of many, and induces them to acquire the licence. It is a matter to be regretted, that, in no few instances, the public do not yet distinguish the qualified from the wholly unqualified members of the profession; but another decade will, doubtless, lead them to appraise at their true worth a class of men whose conduct brings a blush of shame upon the face of every respectable practitioner when he hears them called by the same title as himself, and it is deplorable that journals of reputation can be induced to insert the specious and lying advertisements of such men as those to whom we refer. Only by insisting on the highest standard of professional knowledge and the strictest code of social ethics in our educational establishments can we teach the public to discriminate between such men and those deserving their confidence.

No man has contributed more to the literature of dental surgery than Mr. Tomes, and it is with great pleasure that we see another edition of his book, in producing which he has been aided by his son, Mr. C. S. Tomes. The present volume is in every respect an improvement upon its predecessor, the important additions to its text proving the great advance which has been made in the science of which it treats since the publication of the first edition in 1859. All the sections of which the book is composed have been carefully revised, especially those relating to the development of the dental tissues and to the description of caries; whilst those on neuralgia, odontomes, hyperostosis, and those indirect affections connected with dental disease, are entirely new. Notwithstanding these additions, however, the book is not a ponderous one, inasmuch as the size of the print has been materially reduced. The first 250 pages of the book are devoted to the subject of teething, that is, the condition of the teeth and jaws at the time of birth, and the changes onwards until the temporary teeth have arrived at maturity. The subject matter here is much the same as in the earlier edition, which seemed even then to be almost exhaustive of the topic, as far as development was concerned; and, if a fault could be found, it would be that the latest improvements in the mechanical treatment of irregularities of the teeth have not been described quite so fully as they might have been; this, however, is a small matter where so much that is valuable is to be found.

The section on the dental tissues has been almost entirely rewritten, and the list of works referred to, given at the head of the chapter, alone prove how thorough has been the research after every available source of information. Here we must

allude to a most interesting discussion as to the histological importance of the so-called membrana preformativa. Mr. Huxley was the first to discover that this membrane could be raised 103-LII.

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from the enamel at any period of its growth by the use of hydrochloric acid, and, as he considered his discovery proved to him the existence of a well-defined membrane separable both from the enamel-pulp and the enamel, the question occurred whether the enamel organ really has any influence in the development of the enamel, Mr. Huxley maintaining that neither it nor the capsule "contribute directly in any way to the development of the dental tissues, though they may indirectly." Kölliker and Wenzel hold a different view entirely and assert that the enamelcells do not undergo conversion into enamel-fibres, but that the enamel is secreted from their ends. Now, Mr. Tomes thinks that the enamel-cells are actually converted by calcification into the enamel-prisms, the periphery of the cell being calcified earlier than the central portion. Whilst calcification is thus proceeding inwards in each individual cell it unites the contiguous cells to each other. At this point, viz. the remotest line of calcification, the cells are easily withdrawn from the calcified fibres, leaving the surface of the latter with the appearance of a perforated membrane, these perforations being caused by the withdrawal of the inner uncalcified portions of the cells or columns. Now, it must be remembered that this membrane can only be demonstrated by the action of a strong reagent, viz. by an acid capable of dissolving calcium carbonate and phosphate, and we think that, considering this fact, its substantial existence is at least open to doubt. In fact, Mr. Tomes's clear explanation of the development of the enamel-prisms from the columns of the enamel organ almost conclusively proves, that this membrane is to be regarded only as the youngest layer of enamel but slightly impregnated with inorganic constituents, and as having no connection whatever with the formation of the enamel.

Some years ago, it may be remembered that Professor Owen entered into a warm controversy with Mr. Nasmyth concerning a membrane which has long been known by the name of its professed discoverer. "Nasmyth's membrane" is a tissue separated from the surface of the enamel, and has been therefore called the persistent dental capsule. Waldeyer considers it to be formed. from the external epithelium of the enamel organ, metamorphosed into cornified tissue, as a proof of which theory he states that the remains of cells can be seen by staining with nitrate of silver. Huxley considers it to be identical with the membrana preformativa; whilst Kölliker, following out his favorite excretion theory, thinks that it is a protective covering thrown out by the enamel-cells over the enamel. On the other hand, Mr. Tomes, arguing upon the fact that this membrane is continuous with the cementum of the fang, and that it is thickened in the depres

sions of the crowns of molar teeth, considers "Nasmyth's membrane" to be nothing more than a thin layer of cementum, the absence of lacunæ in its substance being owing to the fact of its extreme thinness. Mr. Tomes has made many observations on numerous specimens since the previous issue of his book, and they have led him to feel even more confident of the correctness of his views than before. Hence, if they are accepted, and Mr. Tomes's explanation of the appearances presented certainly appears more lucid than any yet given, we must look upon this membrane as cementum either imperfectly calcified or not yet calcified at all; but, at the same time, it must be recollected that there are many analogies for assuming it to be a kind of finishing coat to the enamel, as Kölliker supposes it to be.

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One of the most interesting chapters in the book is that on "Odontomes," and it is probably the most perfect memoir on the subject existing; for besides many original remarks it sents a most instructive résumé of the views held by various authors on the subject. The term odontome is applied to those masses of dentinal tissue which result from morbid conditions of the formative pulp, and may be divided into four classes, according to Professor Broca's classification, viz. "odontomes embryoplastiques," those which arise before the development of the membrana eboris; odontomes odontoplastiques, or those arising before the first layer of dentine is formed; and odontomes coronaires and radiculaires, or those which arise during the formation of the crown and root respectively.

This subject is of the greatest interest to the surgeon, for this is a class of tumours the character of which has hitherto been wholly misunderstood, so much so that terrible operations have been performed for their eradication under the supposition that they were osteal tumours, but which, had their true nature been appreciated, need never have taken place. The peculiarity of these tumours is that they are encysted in the bone of the jaw, having no continuity of structure with the surrounding tissue. On examination they are seen to be made up of a heterogeneous mass of enamel, dentine, and bone-like material. In the odontoplastic variety there is often, on a merely superficial examination, but little resemblance to a tooth, but in the odontome coronaire, which originates after calcification has commenced, the crown at least is fairly formed, mixed up, though it be, with subsequent outgrowths of the pulp. Now, large portions of the jaw have been resected under the belief that there were tumours connected with its substance, whereas, had their true. character been known, only a small portion of the bone need have been removed, sufficient to expose the mass, which would then have been easily extracted, its removal being followed by the relief

of all the symptoms, the cavity in the bone speedily contracting and filling up, leaving but little trace of the operation behind.

What are the means by which these growths may be identified prior to removal? In every case one or more teeth have been noticed to be absent from the normal series; and in all those cases where there is enlargement of the maxilla, and teeth are found never to have been erupted, there is a strong antecedent probability that the absent tooth is the cause of the tumour, and there is but little doubt that, had this fact been always remembered, many jaws might have been saved and the odontome removed with very little destruction of the bone. We have not sufficient space to enlarge upon this interesting subject, but may briefly say that this chapter is as pregnant with interest to the general surgeon as to the specialist.

The next chapter is devoted to the consideration of those peculiar cysts found in the substance of the jaw containing a tooth or teeth, and, therefore, called dentigerous; and although more easy to diagnose than the odontome, they have still been at times mistaken by the surgeon. Much discussion has arisen as to their true character, and Mr. Tomes, though regarding the question as still in abeyance, seems to incline to the viewthe correctness of which mainly depends upon the assumption of the presence of Nasmyth's membrane on the enclosed teeththat the fluid contained in the cyst lies between the enamel and the tooth-capsules. This opinion has been promulgated by Mr. Salter, though we know not to whom the credit of its origin must be conceded.

The section on neuralgia is also, like the two preceding, one of general interest, and Dr. Anstie's views upon the subject are somewhat sharply criticised. The opinions concerning the pathology of neuralgia are very various, and Dr. Anstie maintains that the posterior roots of the spinal nerves are the real seat of mischief, and that the essential condition is atrophy, which is usually non-inflammatory in its origin. With regard to this view Mr. Tomes remarks that it scarcely seems tenable when experience daily teaches us that the extraction of a tooth, or even the destruction of a nerve by an escharotic may effect the instantaneous cure of long-standing neuralgia; for this fact seems of itself to prove that neuralgia is possible without much central degenerative change. With respect to Dr. Anstie's disbelief in carious teeth being a frequent source of the disease, it is remarked that few dental surgeons could endorse it, though Mr. Tomes excuses it by saying that many of the most typical cases of neuralgia, as produced by diseased teeth, are just those in which from the absence of all local pain the teeth are never subject to suspicion. We ourselves wonder that a careful observer like

Dr. Anstie could have hazarded such an assertion; and, indeed, not to mention innumerable other cases, we have just seen one where acute neuralgic pain over the left parietal bone, which had existed for nearly two years, was instantly cured by the extraction of a carious first molar which had never been suspected of being the causa morbi, inasmuch as it had never itself exhibited the slightest local pain. We are certain that if those who are called upon to treat seemingly intractable cases of cranial and facial neuralgia would pay more attention to the condition of the teeth they would often find the straight road to successful treatment of the malady. Likewise in the chapter succeeding that which we have just commented upon, many secondary affections are mentioned which had their primal origin in diseased conditions of the teeth, those affections varying from the simplest neuroses to amaurosis and paralysis.

We now come to the consideration of the pathology of dental caries, and here Mr. Tomes not only gives a most clear and lucid exposition of his own views on the subject, but has added an appendix at the end of the volume which enters fully into the opinions of other writers, and from which certain deductions are drawn which will be alluded to presently. On the causes of decay of the dentinal tissues various theories have been advanced; some maintaining that the destruction of tissue is mainly dependent upon chemical action, others regarding it as strictly a vital phenomenon, while others, again, argue that it is the result of combined chemical and vital action. In comparing the chapter in the first edition of this book relative to these different opinions with that in the present volume, it appears that Mr. Tomes's views have undergone some modification; he then seemed to side with those who argued that a combination of chemical and vital forces caused the disease, summing up his case by saying that whilst there could be but one opinion as to the mere chemical character ofthe processes by which the enamel and dentine are softened by the removal of earthy matter, that this process was to be regarded as a "consequence secondary to some preceding change in the part rather than as a primary condition." He now comes to a different conclusion, viz. "That caries is an effect of external causes in which the so-called ' vital' forces play no part," a conclusion which in the present state of our knowledge-which must as yet be deemed imperfect-does not seem to be quite warranted by facts, especially as the views of the chemico-vital party have been rather kept out of view in the controversy, the arguments in the appendix seeming to us particularly biassed and inconclusive. It would be out of place to discuss this question in extenso here, but some pathological phenomena which are described by Mr. Tomes appear to militate against the view