Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/395

 PATHOLOGY 373 of a common starting-point for structures that come to be very unlike. We may note, among other things, how small a step there is from the production of blood and blood -pigment on the one hand to that of hair on the other. 1 5. ERRORS OF DEVELOPMENT AND GROWTH IN GENERAL. The more iisual departures from the normal type in the embryological rudiments or in the growth of particular organs and parts of the body have been already described in the article MONSTER. The present section will be de voted to those errors of development and growth which amount practically to constitutional diseases.
 * kets. Rickets. We have hitherto considered the indwelling spon

taneities of the cells and tissues as manifested in the process of repair, and manifested capriciously in some tumour-processes ; in these it has seemed as if the blood-making function of the embryo were the most fundamental of all its primitive tendencies, traces of it being found in the reparative process and in the new growth of tumours. Xext to it, and even bound up with it, is the bone-making function ; and we now come to a general or universal disorder of the bone-making function in which these developmental doctrines will be found to have a useful application. This disorder is rickets, a common malady of infancy and childhood. Attention was first drawn to it in 1650 by Glisson, who spoke of it as a disease of children that had been known to be endemic for thirty years in Somersetshire, and had been brought from the country to London. It is very common in all great cities ; in A T ienna it is still known as &quot;die Englische Krankheit.&quot; A child developing this error of growth becomes profoundly affected in its health generally. It is tender all over, dislikes to be touched or handled, throws off the bedclothes even in cold weather, perspires profusely about the head, moves its head restlessly in sleep, so as even to wear the hair off, and in its waking hours sits perfectly still and subdued under a kind of suffering which can be but half -realized by its. con sciousness. Such children give little trouble, seldom crying even when left alone. They are very sensitive to cold, and proportion ately liable to catarrh ; their nervous impressibility also is height ened, making a peculiar liability to convulsions and to laryngismus stridulus. They are &quot;backward children,&quot; and, in particular, late in getting their teeth. &amp;gt;e- The conspicuous error in such subjects is in the growth of the th bones everywhere throughout the body. The rickety condition often begins in children who are plump and apparently well ets. nourished ; and, if the nutritive and other processes are involved at length, it is the osteoblastic process that is primarily at fault. The details are somewhat different for the two kinds of ossifica tion in membrane or periosteum, and in cartilage. Regarding the former, the error will be readily understood by reference to the accompanying cut (fig. 38) of normal ossification of the FIG. 88. Ossifying parietal bnne of total kitten, a, a, spindle-celled mem brane, corresponding to periosteum ; 6, spicule of calcified ground-substance, with free osteoblasts at one end and imprisoned bone-corpuscles at the other ; c, broader bars of bone. parietal bone. The spindle-cells of the membrane are becoming cubical along a line a little below the surface, and a few of them are half-included or imprisoned in the thin bar of bone ; most of them are free on the surface of the calcified bar, as osteoblasts, the included ones being bone-corpuscles. Increase of the osseous tissue takes place through other osteoblasts becoming surrounded by cal cifying ground-substance ; and, in the broader bars of bone below, the bone-corpuscles may be seen to be two or three rows deep. This process goes on until the whole of the osteoblasts (derived from spindle-cells) have been included one by one within the calcifying matrix ; once included, these cells are incapable of growth ; the multiplication is always in the spindle-shaped cells of the membrane, or on the surface of the bony bars or trabeculrc ; and the inclusion 1 See Virchow, Die krtcnkhnjten Geschwubte, 3 vols. , 1 863-67 ; Paget, Surrj. Path.; Cohnheim, Varies, iiberally. Pat/wl., vol. i. p. 622 ; Rud. Maier, Lehrb. der ally, patlwl. Anatomic, Leipsic, 1871. is of that gradual and co-ordinated kind that there is always a st t of free cells left on the surface to keep up the succession of formative elements. It is not until growth is completed that osteoblasts cease. The error in rickets is that the multiplication of spindle- shaped cells and osteoblasts far outruns the calcifying process. Instead of these elements being produced only as fast as they are wanted for inclusion as bone-corpuscles, they are produced regardless of the forwardness of the calcifying process, upon whose exact co-operation with the cellular formative process all true periosteal bone-making depends. The error, or part of the error, of rickets is that the calcifying process is behindhand. A large quantity of soft bone-making material accumulates, which would, under ordi nary circumstances, have become hard bone as soon as it was formed ; sooner or later it becomes bone, even, in rickets, but the deposition of earthy salts is slow, and in the meantime the bones have be come bent. Not only is there a relative, slowness in the calcifying process, but there is an absolute excess of the cellular elements or of the osteoblasts ; and, in the flat bones of the skull, this is shown in the thickness of the bones ultimately, especially along their growing edges. The same excess of formative material beyond what can be used up for bone is seen in the ossification from carti lage at the epiphysial line. The cartilage-cells divide and multiply at an excessive rate, and the columns of them, instead of keeping in the line of the axis of the bone, radiate to the sides, so that there is often a bulbous enlargement where the epiphysis joins the shaft. The want of harmony in the calcifying and osteoblastic parts of the process is shown by the irre gularity of the epiphysial line (fig. 39) ; it is a straight line normally, but in rickety growth it runs out and in, cutting off islands of car tilage in the midst of spongy bone ; and this irregularity is due to the fact that the blood-channels in the cartilage are formed sooner at some points than at others, the calcifi cation following close on them. In the shaft of a long bone the process is the same as in a flat membrane- bone of the skull ; the periosteum , is thick and its inner layers are V&quot; blood -red, and in extreme cases there is what looks like a stratum of blood between it and the bone. Bone is at length formed from this layer, but it is of the spongy kind, so that the shaft is softer and more porous on the outside than on the FIG. so. Lower end of femur &amp;lt; f baboon with rickets, showing the broad and irregular epiphysial line of growing cartilage (white), with spongioid tissue above it and islets of cartilage in the spongy bone be neath, a, a, a; 6, &, irregular epi physial line of cartilage. (From J. B. Button, in Path. Trans., xxxiv.) inside. In the fat bones of the head, also, the structure is apt to be of the spongy kind throughout, so that they consist as if of diploe entirely, and not of a layer of diploe between two hard plates. Sooner or later, under favourable circum stances, the spongy bone is replaced by compact bone, and in th&amp;lt;~&amp;gt; end the bones of a rickety subject are harder and thicker than usual. In the worst cases deformities remain, notably the bent spine, the pigeon-breast, and the deformed pelvis. In the very worst cases the stature is dwarfed and the long bones are bent and twisted. Analysing these phenomena and filling in details, we come in the last resort to an indwelling disposition, probably acquired in most cases, or in largest measure, before birth. These tendencies come to an issue in the skeleton, because the growth of the bones is of a nature to tax the organism. The growth of the bones is the great instance of metaplasia; it is a succession of tissue - changes long kept up, and it requires a peculiar co-ordination or orderliness at each step, owing to the fact that stiffness has to be combined with plasticity. The requisite stiffness can only be got step by step through the sacrifice of that plasticity which goes with growth, and hence the special adaptation of a free row of osteoblasts on the surface of bone-trabeculrc to ensure the apposi tion of new layers. Cartilage gives the stiffness for a time in all the bones except the clavicle and those of the vault of the skull ; having served its purpose, it becomes spongy bone, blood, and marrow, the spongy bone being finally removed in the shafts of long bones, the marrow remaining, and the blood continuing to be added to the general blood of the body. In these adaptations the early importance of blood-making among the embryonic cells is duly asserted. When the fretal cartilages have served their turn the hrematoblastic function becomes prominent in the cells, and a large part of all that was cartilage literally becomes blood. Accord ing to numerous observers, it even becomes blood without the accompanying formation of blood-vessels with definite walls. Some of it becomes bone ; but the bone is in thin plates only, and much of it is ultimately removed. In the periosteal process, also, where the cartilage-stage of the formative tissue is never gone