Rickets (Rhachitis Juvenilis In Contradistinction to rhachitis adul-torum and rhachitis senilis, which are equivalent to mollities ossium) is a disease of early childhood. It is, in most cases, developed first in the lower extremities: after having reached a certain degree in them, it extends to the pelvis; and advancing from thence to the other bones of the trunk, it at last pervades the whole skeleton. Sometimes it is more prominently marked in one portion of the skeleton, while the rest of the bones are but slightly affected; and then a rickety thorax or skull constitutes nearly all the disease. It is combined with preternatural development of the glandular system, with hypertrophy of the white substance of the brain, with deficient involution, or even with hypertrophy of the thymus gland, with hypertrophy of the spleen, spare muscular development, and a pale and flabby condition of the muscular fibre. It is associated with tubercle very rarely, considering that the deformity of the thorax which rickets frequently occasions, brings on conditions suited to the development of that disease.

It interferes with the growth of the bones in length, and with the development of certain portions of the skeleton in their proper relations as to capacity. Some of the deformities which it occasions are produced only in this way, such as shortness of the long bones, and narrowness and small size of the pelvis; whilst sometimes there are other conditions which essentially co-operate in effecting them. Thus the weight of the body pressing perpendicularly on the pelvis and lower extremity gives rise to the sabre-shaped curvatures of the latter, and the flattening anteriorly, the narrowing of the conjugate diameter, and the great inclination of the former; and this is the case whether the deformity be symmetrical on the two sides, or whether it predominate on one side, and the pelvis be oblique or inclined. Lordosis or scoliosis of the vertebral column follows upon the deformity of the pelvis, and the degree of either is proportioned to that in which the vertebrae are affected with rickets. Consequent upon the deviation of the spinal column from its natural direction, ensues corresponding deformity of the thorax. If the muscles of the thorax - the pectorales and serrati - be in a very undeveloped state, a deformity results which is known by the name of the (rickety) pigeon's breast. In the skull, the hypertrophy of the cerebrum, especially of its anterior lobes, moulds the bone into the peeculiar corresponding shape. The necessary description of all these changes will be given hereafter; only it must be remarked that, as the deformities which are produced by rickets in the lower extremities and the trunk, depend upon causes that vary much in the degree, the duration, and the manner of their action, so they do not follow constantly any definite type, but rather present, especially in the pelvis, frequent exceptions to any forms which may be set down as the rule.

The bones appear swollen out; the angular shaft of the long bones becomes round and cylindrical; and their articular extremities, as well as other broad bones which contain much diploetic tissue (such, for instance, as the bones of the pelvis), become unusually thick.

The texture of the bones is affected in two ways, of which sometimes one preponderates, sometimes the other. In the first case the bone is rarefied and increased in size - expanded in fact. A pale yellowish-red jelly is effused into its enlarged canals and cells, into the medullary cavities, and even under the periosteum. The bone itself is abundantly supplied with vessels and full of blood, and its color is therefore darker than natural, and red. Occasionally this change reaches such a degree that the cells of spongy bones, and those in the interior of medullary tubes, become excessively distended, and, as their walls disappear, are merged in larger cavities: medullary cavities at last become single spacious chambers, and the bones uncommonly soft and fragile (Guérin's Con-somption Rachitique). In the second case the bone is, in addition, deprived of more or less of its mineral constituents; and sometimes it is completely reduced to its cartilaginous element, and appears like a bone that has been steeped in acid. The bony corpuscles are empty, and their rays have disappeared, and when this is the case, the lamellar structure is here and there obliterated; at other parts the lamellae appear as it were, to have fallen asunder, and the corpuscles are seen quite distinctly interposed between them. It is upon this condition that the softness, the flexibility, etc, of rickety bones depends.

These two conditions exist together, as has been remarked, and sometimes one preponderates, sometimes the other; it is, however, remarkable, that in cases of general rickets, the reduction of a bone to its cartilaginous element so preponderates in some bones as to go on, even to completion, without any trace of rarefaction.

The periosteum of rickety bones is palpably more vascular than natural, and tumid; it clings to the bone so closely that a layer of the expanded spongy tissue always comes away in the attempt to strip the membrane off.

Rickets

Rickets is not a painful disease. It is usually developed in the second year of life, and leaves traces behind it corresponding to the degree it had attained. In small degrees it is capable of cure by the reabsorption of the substance which has been effused into the cavities of the bone, and the subsidence of the swelling of the bone. In more advanced degrees the cure is effected by that substance becoming more and more firm, and at last ossifying. The bone then remains enlarged and becomes uncommonly dense (Guérin's Eburnéation), and the Haversian canals contract, especially on the concave side of the curves. When the disease reaches its highest degree, the rarefaction which it has occasioned and the fragility of the bone are permanent.