PATHOLOGY " cvst. Fie. 35. Myeloid tissue it began as a temporary fatal cartilage ; it then became spongy l>oue tilled with red marrow, in which state it remains in the ends of long bones, in the diploe of flat bones, and in the in terior of bones like the vertebra. . In the shafts of lov.g bones the trabecul* of bone are all removed and only u-d marrow remains, with a pronounced ha-matoblastic function ; but, when growth is well advanced, the cells of the ml marrow become exca vated to fat-cells, their blood-forming function ceasing therewith. We have also seen that, in the process of repair, the marrow and its blood-vessels together are able to produce new bone between the broken ends. There are here memories enough to produce very fantastic results if anything should arise to recall the develop mental activity. Disregarding the livid or blood-like patches, the mucous areas (whether myxouiatous tissue or colloid fluid and the fragments of cartilage and of osteoid tissue, some of which have been spoken of above, let us consider the tissue that is most characteristic of this group of internal bone-tumours. It is the yellowish or sand-coloured areas of friable texture, corresponding to the tissue named by Paget "myeloid," or marrow-like. Its name is due to the fact that it always contains a number of multiuuclear cells, giant-cells or myflopkurts, such as are found in the marrow of young bones. Its yellow ish colour is almost sufficient of itself to indicate the presence of these elements. The cut (fig. 35) shows several of t;. myeloplaxes lying among cells of various shapes with a single nucleus. In oue^direction it is no great step from this to myxo- inatous tissue or other luematoblastic modifications ; and in another direction it is no great step back to cartilage. "We shall probably not go very wide of the mark if we take the common starting-point of the various tissues to be fcetal cartilage, as drawn in fig. 30 from an enchoudroma of the upper jaw ; and, given fo?tal cartilage, it is not difficult to follow it along the various lines of its historical development in the shaft of a bone, to imagine the development taking a devious turn -at one point or another, and so to account for the heterogeneous structure of the tumour, some of the structure, indeed, being strange to the normal types of growth. Drrmoid Cysts. Having now illustrated two great instances of embryonic function revived in after life to the production of tumours namely, the blood-making and the bone-making functions and having therewith disposed of a considerable number of all the tumours that have a mesoblastic homology, it will be convenient to advert to a remarkable kind of tumour which shows to the fullest extent what the embryonic mesoblast can do in the way of fantastic new productions, namely, dermoid cysts. Not only blood and bone, but teeth, skin, hair, glands, muscle, and nerve are pro duced as the tumour-constituents in these remarkable new growths. Their usual seat, and the invariable seat of the most perfect of them, is the ovary ; and the ovarian is just that mesoblastic tissue upon which the memories of development are as if concen trated ; for it is from an ovarian cell that the embryo grows in the perfect likeness of the parent These selected cells of the ovary, or, in other words, the ova, are specially charged with the recollec tions of the past history of evolution and growth ; and the rest of the ovary appears to possess the same lively memory, if not to the same extent, yet to a much greater extent than mesoblastic tissue elsewhere. The stroma of the ovary is the best example in the body of embryonic spindle-celled mesoblast ; only in some animals doe* it become normally fibrous, and in any animal it may revert to embryonic characters with the greatest ease at the generative periods or at other times, and even in extreme old age. But for the fact that the tissue keeps within normal limits of form and extent it might pass muster for spindle -celled sarcoma, in all respects, including the warp-and-woof arrangement of the tracts of eeDa. From this tissue cysts are developed interstitially. and they are not the less interstitial in their development that their homo- logue is often, if not always, a Graafiau follicle. That, however, is a region of controversy, and it will be more convenient to take an unambiguous case first Such would be a dermoid cyst under the skin, say in the neighbourhood of the orbit It is "true that even these cases are sometimes explained by assuming that the skin has somehow become involuted at the particular spot during development ; but no observed facts warrant this assumption, and the histogenetic facts of the new growth itself are entirely against it. Fig. 36 shows a portion of new -formed skin on "the wall of a small congenital dermoid cyst over the external angular process of the frontal bone : adjoining the actual skin there may be seen the interstitial cells of the connective tissue becoming adapted in form and arrangement to continue the layer of rete mucosum over the cyst -wall beyond- The adaptation is very much the same which has already been mentioned with reference to the new skin of a granulating surface ; the connective-tissue cells become large and cubical, often multinuclear, and elongated towards FIG. 36. Wall of dennoid cyst, showing how the surface-stratum is produced from interstitial connective-tissue cells. the surface. The supply of these formative cells comes from the connective-tissue elements lying among the parallel fibrous bundles of the cyst-wall. For a dermoid of the ovary it is impossible in a brief space to give any idea of the marvellous textures that are being woven side by side in various parts of the cyst-wall, the areas of fcetal cartilage, the interlacing bundles of plain muscular fibres, the long rows of pigment-cells, and, not far off, the rows of mucous cells developed iuterstitially, and maturing so as to be fused into the fluid of sub ordinate cysts. At one place there is a piece of skin, underneath which will be found an enormous development of sebaceous glands ; where the skin ends a brownish velvety patch begins, with no sebaceous glands, although there are rudimentary hairs at various depths. This under the microscope will IK- found to approximate to granulation-like tissue, with many variously-shaped pigment-cells, and corresponding probably to the congenital mother-marks of the skin proier. It must suffice to give a single illustration of the strange formative activity of this mesoblastic tissue, namely, the formation of hairs. Hairs in dermoid cysts are formed in a very Hairs peculiar manner. It is usual in subcutaneous demioids to find them derm embedded parallel to the surface at various depths in the midst of cysts, multiuuclear or giant -cells. Some of these multiuuclear masses may be seen undergoing a vitreons transformation down the middle, as in fig. 37, a ; elsewhere may be seen the same peculiar central rod extending through a succession of giant - cells : and, most remarkable of all, there is the appearance drawn in c. In this last case the vitreons rod is capped at each cud by a giant -cell, and the $flr characteristic imbrication of scales has developed on it over the intervening length. The cross section of such a hair is seen in d. The section of hair is evidently a part of the multinuclear cylinder ; it is in this instance well to one FlG - 37.- n. vitreons trs: i i . ... - .-,1 , , central line in interior of giant - cell ; b. side, but it is still enclosed *, hairs lying among giant ils in wall of by the marginal nuclei of the dermoid cyst ; c, hair in dermoid cyst, cell, which are flattened into capped by giant-cells ; rf, cross-section of plates upon it ; in other in- * fef r J^f utetanCe f * ?iant - ce11 ( ier , f 11- -."" stances it is found lying out side the largest of a cluster of giant-cells and surrounded by the smaller ones. The nature of the transformation in the heart of these multinuclear blocks is not easy to determine; the most striking circumstance is that other giant-cells, which appear to be advancing in the same direction, or to have diverged from the same kind of development, have an area of deep-brown or orange pig ment in their centre instead of the vitreous or horny transforma tion, the marginal belt being free from pigment. This is a ]K-culiar formative use of giant-cells. We have already seen that they are used in the vessel-making processes of the placenta and of rejtair ; we have seen also that they may be the media through which a granulation-surface acquires a covering of epidermis ; and here we find them playing the part of hair-follicle. A dermoid cyst reveals the surprising spontaneities of a collec tion of embryonic cells of the mesoblast, the inherited traditions of their life, manifested in diverse ways side by side, and mani fested often feebly and grotesquely. There is no reason to seek for the source of these various products beyond the stroma of the ovary itself ; and the variety of the products must be a measure of what that kind of tissue can do in the way of new formation. When various kinds of structure are thus brought together in their de velopment we have an evidence, not only" of the indwelling power of mesoblastic tissue to revert to embrvonic modes of life, but also
