The vertebral column suffers also. In the normal infant it is straight, but in the rachitic it exhibits a kyphotic deformity very soon. When such a baby of three or six months is sitting up, the middle portion of the back is protruding, as in Pott's disease. In almost every case, however, this kyphosis is but apparent and the result of muscular debility. In order to arrive at a diagnosis at once, it is sufficient to place the patient on his face and support the head, and raise the lower extremities and pelvis in the air. If the kyphosis is but functional, the prominence disappears at once. By nothing can the muscular insufficiency of early rachitis be better demonstrated than by this little experiment. But actual deformity is also found in rachitis. It softens both the vertebræ and intervertebral cartilages, and either their anterior or posterior portion may be irregularly developed, and be either too high or too low. Besides, the articulating surfaces are sometimes too convex. Thus the causes of both kyphosis and scoliosis are amply furnished, and complications of the two are quite frequent, and the deformities resulting therefrom quite formidable. Scoliosis is mostly to the left; kyphosis generally complicated with lordosis, and sometimes the vertebral column exhibits a spiral shape. The ribs of the convex half are prominent and divergent, those of the concave side flattened and parallel. The two halves of the chest are therefore very unequal indeed. Muscular traction, atmospheric pressure, {152} the elastic traction of the lungs, the presence of pulmonary complications, and the pressure from below on the part of the enlarged viscera of the abdominal cavity, come also in for a considerable share in the completion of the deformity.