onstitutional disease associated with
disturbance of nutrition, and attended with changes in the skeleton.
The disease is most common and most severe among the children of the
poorer classes in large cities, who are improperly fed and are brought
up in unhealthy surroundings. There is evidence that the most important
factors in the causation of rickets are ill-health of the mother during
pregnancy, and the administration to the child after its birth of food
which is defective in animal fat, proteids, and salts of lime, or which
contains these in such a form that they are not readily assimilated. The
occurrence of the disease is favoured, and its features are aggravated,
by imperfect oxygenation of the blood as the result of a deficiency of
fresh air and sunlight, want of exercise, and by other conditions which
prevail in the slums of large towns.

_Pathological Anatomy._--The most striking feature is the softness
(malacia) of the bones, due to excessive absorption of osseous tissue,
and the formation of an imperfectly calcified tissue at the sites of
ossification. The affected bones lose their rigidity, so that they are
bent under the weight of the body, by the traction of muscles, and by
other mechanical forces.

The _periosteum_ is thick and vascular, and when detached carries with
it plates and spicules of soft porous bone. The new bone may be so
abundant that it forms a thick crust on the surface, and in the flat
bones of the skull this may be heaped up in the form of bosses or ridges
resembling those ascribed to inherited syphilis.

In the epiphysial cartilages and at the ossifying junctions, all the
processes concerned in ossification, excepting the deposition of lime
salts, occur to an exaggerated degree. The cartilage of the epiphysial
disc proliferates actively and irregularly, so that it becomes softer,
thicker, and wider, and gives rise to a visible swelling, best seen at
the lower end of the radius and lower end of the tibia, and at the
costo-chondral junctions where the series of beaded swellings is known
as the "rickety rosary."

The ossifying zone is increased in depth; the marrow is abnormally
vascular; and the new bone that is formed is imperfectly calcified. The
result is that the bones may never attain their normal length, and they
remain stunted throughout life as in rickety dwarfs (Fig. 133), or the
shafts may grow unequally and come to deviate from their normal axes as
in knock-knee and bow-kne