It seldom begins before six months or after three years.

There are several theories as to its causation, one being that it is due to an abnormal development of acids.

There is little doubt that defective nutrition and bad hygienic surroundings are prominent factors in its production.

The principal pathologic change is seen in the epiphyseal lines of long bones and beneath the periosteum.

Figure 213 shows the appearance during life of a patient with the highest grade of rachitis, and it can be easily understood what a barrier to natural child-birth it would produce.