The urine contains an increased proportion of phosphate of lime, and lactic acid has been found in it by some observers. The secretion is pale in colour and often deposits crystals of oxalate of lime. Often, also, as is so commonly the case in children in whom acid is largely generated from fermentation of food, crystals of uric acid and even considerable quantities of red sand may be passed from the kidneys.
In addition to the above pathological conditions, which may be con sidered to arise directly from the general disease, there are others which may be looked upon as accidental since they are induced mechanically by the deformities of the thorax resulting from the softening of the ribs. In all cases of distortion of the framework of the chest two pulmonary lesions are invariably present. These are emphysema and collapse. The emphy sema is seated at the anterior borders of the lungs, and extends backwards for about three-quarters of an inch from their free margins. Immediately outside this line of dilated lung tissue is a line of collapse which separates it from the healthy pulmonary substance beyond. These lesions occur to gether and, although not dependent one upon another, are produced by the sank mechanical means. During the act of inspiration the softened ribs sink in, and the pressure of the enlarged ends of the ribs compresses the lung tissue with which they are in contact so as to prevent its expan sion by the air which inflates the remainder of the lung. While, however, the diameter of the chest is narrowed laterally, its antero-posterior diameter is increased by the protrusion of the sternum. Consequently the alveoli of the anterior borders, immediately behind the breast-bone, are dis tended by the air which is forced into this part to fill up the resulting space.
Pulmonary collapse is not always limited to the parts of the lung cor responding to the ends of the ribs. There is often to be seen, in addition, a certain amount of atele.ctasis at the bases of the lungs behind. Collapse at this part of the lung is due to pulmonary catarrh and plugging of an air-tube with mucus. Its mechanism is described elsewhere (see p. 465).
The enlarged epiphyses of the ribs, besides their effect upon the lung tissue, are also the cause of the patches of circumscribed opacity seen on the visceral surface of the pericardium and on the spleen. That on the
pericardium is situated on the left ventricle a little above the apex of the heart. At this point the heart at each beat comes into contact with the nodule of the fifth rib. That on the spleen is produced in the same way by attrition, the organ as it rises and falls in respiration being rubbed against a similar costal projection. In each case the white patch is limited to the fibrous layer.
From a consideration of the morbid changes discovered in the bodies of rickety children, it is evident that the disease is a very special one, in volving very wide-spread lesions of structure. Attention has lately been directed to the whole subject of bone changes in the young subject, and it is asserted that many cases in which bone softening has been pronounced are not real examples of rickets, but ought rather to fall under the head ing of osteo-malacia ; the osseous changes resembling closely those observ able in cases of osteo-malacia in the adult. The question is of importance, for the pathology of the two conditions is essentially dissimilar. In osteo malacia softening is the consequence of a removal of the earthy constitu ents from perfectly formed bone. In rickets ossification is incomplete, and much new material is thrown out which undergoes very imperfect calcification. The question can only be decided by a careful study of the morbid appearances. In the case of a rickety little girl, aged eighteen months, described by Dr. Rehn of Frankfort, there was marked distortion and softening of many of the long bones, with other signs usually consid ered characteristic of rickets. The disease, however, was judged to be osteo-malacia on the ground that although softening was a marked feature in the bones, the epiphyseal ends were only moderately swollen, and in the bones of the lower extremities were hardly swollen at all. Moreover, the whole skeleton was excessively thin and the lower extremities were quite straight. There was, however, a considerable formation of soft peri °steal deposit ; and a rickety element in the case was admitted. It is pos sible that true osteo-malacia may be grafted on a case of rickets, as is supposed by Dr. Rehn to have happened in the instance referred to, but further observations are to be desired before any definite conclusion in the matter can be arrived at.