“…on the one hand, in the early stages of evolution of Letterer-Siwe disease one may find destructive skeletal lesions resembling cytologically those of eosinophilic granuloma of bone, and, on the other hand, in its chronic stages Letterer-Siwe disease takes on the aspect of Schuller-Christian disease, the skeletal and even certain visceral lesions undergoing lipogranulomatous transformation.' This means that the classification on histological grounds of a given example of the disorder may be difficult, and the literature contains many accounts of illustrative transitional types (Guizetti (1931), Merritt and Paige (1933), Grady and Stewart (1934), Hertzog, Anderson, and Beebe (1940), Curtis and Cawley (1947), Weinstein, Francis, and Sprofkin (1947)). Clinically, however, there is a broad correlation of the different disease groups 97 98 ARCHIVES OF DISEASE IN CHILDHOOD with age, and Mallory (1942) has summarized the position clearly (p. 956) as follows:…”