EVERY specific treatment for a disease makes possible a further differentiation of the conditions that give rise to a similar clinical picture. The widespread use of vitamin D to prevent and cure rickets has made evident the existence of a small group of patients who have most of the developmental manifestations that characterize rickets but who fail to respond to doses of vitamin D that are ordinarily effective in the prevention and cure of rickets.
Vitamin D produces in the rachitic child who is otherwise normal a decrease in fecal calcium and inorganic phosphorus and an increase in the urinary excretion of calcium, with variable effects on the urinary excretion of phosphorus. At the same time the serum inorganic phosphorus rises, and later there is a decline in the alkaline serum phosphatase. The serum calcium rises in children in whom it is below normal. An improvement in muscle tone and