transverse section, the V-shaped appearance," as shown in this photograph.

The removal of the delicate embryonal layers of epithelium by the older methods of preparing specimens leaves the "primitive dental groove" as shown in the preceding illustration. From the inside of this band there grows downward or upward, as the case may be, a thin lamina, from the free edge of which arises the epithelial cord, which, penetrating deeper into the substance of the jaw, enlarges at its lower extremity, forming the enamel cap within which is developed the enamel-pulp. I wish to compare this photograph with the illustration which will follow upon the screen, for the purpose of demonstrating that in point of fact and principle I have shown nothing in my drawings which may not be seen in the photographs from the specimens. (Photographs were then shown of illustrations of former papers by the author in the Dental Cosmos.) And now, just a few words concerning the enamel-pulp or organ before proceeding to review the paper of which mention has already been made. The existence of this important feature of a developing tooth is denied by Prof. Garretson and others, for the reason, I suppose, that their hypothesis makes it necessary that there should be no enamel-pulp.

Gentlemen, the view on the screen (Plate I., Fig. 3) speaks a hundred times more effectively than any arrangement of words, and forever sets at rest this question of an enamel-pulp. This is a photo-micrograph from a section through the jaw of a human embryo, showing the development of a temporary molar. You will observe that the enamel-pulp is, in accordance with what I said in my review of Prof. Garretson's address at Providence, the largest and most conspicuous feature of the tooth-germ in its earlier stages.

As I shall refer to this subject again, I leave it for the present, while I give a few minutes' attention to the paper to which I have already referred. This reprint is largely composed of quotations from different authorities, with comments upon them as to the manner in which hair, skin, hoofs, and horns are formed; an extract from Legros and Magitot; the views, to the extent of half a page, of the expert microscopist already referred to; a brief comment on one of my drawings taken from the Dental Cosmos, and a little more than a half page by the author on the formation of enamel, the subject proper of the paper, and the most of this half page is a description of a drawing made from a slide mounted by Cole, of London.

Assuming that the drawing is a fairly good representation of the slide, it is of but very little value, and the description shows a ludicrous misrepresentation of the little that really can be seen. It is a favorite method with many dialecticians who find a weak cause on their hands to defend, to assume, in a few skillfully arranged sentences, that the hypothesis which they are trying to establish is similar to or identical with, in its relation of principles, some other well demonstrated and generally admitted theory. The most of the time occupied is consumed in dwelling upon the major premise of the argument, which may be nearly or quite self-evident. The mind of the reader or listener is forcibly impressed with the truths presented, and then the minor premise and the inferences or conclusions are rushed in with the flourish of a few well-rounded sentences, and the hearer is overwhelmed before the mind has had time to recover its critical equilibrium sufficiently to see that there are several missing links in the argument. It is a kind of logical trick similar to those with which the Greek school of sophists were wont to amuse themselves. This is quite the case with the paper of which I am speaking. The scheme of argument presented in this paper might be stated as follows: Hair, nails, hoofs, and enamel are epidermoid structures. All epidermoid structures are developed in the same manner. Ergo, the process of the development of hair and enamel is identical. Now, the weak point in the argument arises in the minor premise, which asserts that all epidermoid structures are developed in the same manner, which is very far from the truth. Scales, hair, feathers, nails, horns, hoofs, the enamel of the teeth, the sweat glands, the sebaceous glands, and the mammary glands are all derivatives of the epidermis, but they are not all developed in the same or even in a similar manner. I have frequently urged the importance of some knowledge of comparative embryology in the study of these formative processes. It is impossible to grasp in a rational manner the significance of the intricate unfoldings in the evolution of the higher forms of animal existence without having studied these processes as expressed in a more simple manner in the lower forms. It would be well for these gentlemen, who discourse in a very general way with such a show of profound learning about my reversing the formative processes, disregarding the general physiological laws, and dragging in a divine interposition, to at least give some little attention to the rudiments of these laws themselves, and ascertain, if possible, what they are talking about. There is something about the expression, "a general physiological law,"

which makes it a delight, to men who have only a scanty definite knowledge of a subject, to roll it as a sweet morsel under the tongue. A vast amount of ignorance has many times concealed itself behind "a general physiological law." A little definite knowledge at critical moments is of vastly more value and importance than volumes of brilliant generalizations, which may mean anything, but generally mean nothing.

The ostensible title of the paper in hand is "The Development of Enamel Similar to other Epidermoid Structures." The author would have succeeded much better if he had stuck close to his text. But on page 6 of his reprint, and also on the tenth page, he emphatically declares that the law governing the formation of hair, nails, the cuticle of the skin, the shell of the turtle family, the hoofs of ungulates, and the horns of most of the ruminants, is precisely the same law which governs the formation of the enamel of the teeth. Now, that is precisely what it is not. How any man of sound mind, with healthy, active reasoning powers, could honestly assume that a tissue which is constantly being thrown off and replaced by new tissue-which, when lost, is replaced by a new growth, as is the case with most of the epidermoid derivatives-can be identical in its process of formation with a tissue which never grows after its typal limit is reached, which is never replaced when lost, is quite beyond my powers of comprehension. I might enter into an elaborate argument to show how utterly impossible it is on a priori grounds for the development of enamel to be identical with the formation of hair, but it is much the better way to come straight to the demonstrated facts.

You have on the screen (Fig. 14) a photograph of the drawing in the brochure under consideration, made from the slide mounted by "one of the most celebrated and expert microscopical slide-makers in Europe." It is upon this drawing that he depends for the demonstration of his hypothesis. Now, what are the facts concerning it? It is worse than useless, in the sense that a perversion of truth is worse than the absence of truth. It is misleading to one who has not had experience in the preparation of sections of embryo jaws. It purports to be a section showing the temporary and permanent tooth-germ. The germ of the permanent is entirely absent, as is the enamel, with the exception of a few fragments which were formed on the dentine of the temporary tooth. These portions were probably torn out in the cutting of the section, or washed out in its preparation for mounting. The treatment necessary for the removal

of the water from the tissues previous to mounting in balsam is such that many portions of embryonal and delicate structures are shrunken, distorted, and frequently almost completely destroyed. In this drawing the enamel-pulp, an exceedingly delicate tissue, is so nearly

obliterated as to have little or no significance. The author says, in speaking of the space shown between the dentine and enamel, that it appears in my drawing, and that all good sections show it. Is a "good" specimen one in which all of the tissues are shown in an undisturbed relation? If so, then no good section shows such a

space. It is shown in the drawing referred to, because in all of my drawings I have endeavored to faithfully reproduce the specimen from which the drawing was made, and, where there are defects in the specimens, those defects have been reproduced and explained for the benefit of those who are to follow me in this line of investigation. We sometimes learn more from the failures and defects in our work than we do from our successes, if we but keep our minds open to the reception of truth, at the expense even of a little injured pride. I shall show you photographs and microscopical sections to-night in which these dental tissues are in an undisturbed relation, and where, previous to the commencement of the formation of either dentine or enamel, the dentine-pulp and enamel-pulp are in perfect contact, and also specimens where the first faint lines of dentine and enamel have appeared, and these lines of dentine and enamel in perfect contact, with the ameloblasts everywhere plainly shown above the enamel. In all of the sections which I have cut during the past year there is no appearance of a space between the dentine and enamel until the section is placed upon the slide and the cover-glass pressed down. Then the pressure quite frequently forces the tissues slightly apart. The second illustration of tooth-structure in this reprint is represented as a portion of the previous section more highly magnified (Fig. 15). There is no appearance of an enamel-pulp in this drawing, and what is intended to represent completely-formed enamel is really in the position occupied by the ameloblasts. Below these cells there are probably in the original section a few fragments of the broken and torn enamel. This specimen, as I infer from the text, was submitted to the aforementioned expert microscopist, who returned the following comments:

"A microscopic study of the section of embryonic tooth you sent me discloses the existence of a space between the dentine and enamel. At the base of the enamel, i.e., the surface of the enamel-rods next to the dentine, there exists an apparent line or membrane. Below this line or membrane is a somewhat homogeneous or colloid-looking substance, evidently of much less consistence than the structure above. Above this line is the enamel more fully developed and already hardened." After stating that the supposed line or membrane was an optical delusion, due to angular displacement of the softer portions of the enamel, he further says: "The enamel is formed on the dentine, and develops and becomes indurated as it is elevated by the development of new structure below, precisely as in the case of epidermal cells. I believe the teeth to offer no exception