etiology of rachitis, the periosteal and cartilaginous proliferations would find no explanation. But why is it that this peculiar process takes place at an early age only? and in the bone only? Kassowitz urges the fact that the growth of the bone differs in this from the development of all other tissues: that the latter grow uniformly through their whole mass; that the circulation in them is more uniform and carries material through and into every particle simultaneously, while in the bones the only places in which the whole circulation can contribute to their growth--the few blood-vessels distributed in the interior not adding to their growth at all--are the periosteum and the places of apposition between epiphysis and diaphysis. Every morbid irritation, whether resulting from bad air, habitation, and food, or from either chronic or acute ailment, acts on the whole mass of other tissues and organs, but in the bones only on the growing ends or surface. [Footnote 2: _Anatom. Museum_, Berlin, 1796, vol. ii.] [Footnote 3: _Arch. f. Path. Anat._, vol. v.] The results of the pathologists and experimenters are confirmed by chemical analyses. Fat has been generally found somewhat increased in the rachitical bones, and water largely so; chondrin is diminished according to Marchand and Lehmann, but was found unaltered in the later analyses of A. Baginsky. The latter found, after having deprived the bone of fat, the organic and inorganic material to be in a proportion of 100 to 563 in the normal, and of 100 to 160 in the rachitical osseous tissue; and in 100 parts of dry bone, Gorup-Besanez found in the Ossein. Phosphoric Acid. Lime. Manganese Oxide. Healthy adult 34 26 34 0.3 Infant of six months 34.9 27 35 0.5 Rachitical femur 72 7 9 0.3 " tibia 60 12.9 17 0.3 Defective calcification of the forming bone is one of the principal characteristics of rachitis. In it lime cannot either enter into the composition of the osseous tissue or remain in it. Its elimination must take place either through the kidneys or the intestinal tract. In the feces Ad. Baginsky, and many before him, have found an abnormal quantity. In regard to the urine, modern investigations do not agree with former analyses. Thus, Baginsky concludes that there is no increase of lime in the urine of rachitical as compared with that of healthy children; Seemann found even a diminution of the percentage of lime. Amongst modern writers only Rehn found an occasional increase of lime in the urine of rachitis.