Other explanations have been advanced but up to the present time they scarcely deserve to be regarded even as hypotheses. Thus Anacker in 1865 declared that the disease commenced as muscular rheumatism, was succeeded by destructive or atrophic ostitis, and ended as osteoporosis. So far as the order of the osseous lesions is concerned, this view is quite correct, but the ossific changes are consequences and not causes. The idea that the disease was due to an infectious agent has been advocated by Leclainche, without, however, having been proved. Pétrone is the only person who has hitherto suggested that osteomalacia in man is due to infection with a nitric ferment (_Micrococcus nitrificans_). According to him, pure cultures of this organism injected into dogs, produce osteomalacia. These statements, however, require confirmation. =Lesions.= The chief lesions are to be found in the bones. They consist in rarefaction of the compact tissue, increase in size of the medullary cavity and Haversian canals, and enlargement of the areolæ of the spongy tissue. The bone marrow loses its fatty constituents, appears red and gelatinous, and contains a greatly exaggerated number of blood-vessels. When heated, the bones do not yield oil as in healthy subjects, and when dry, they seem abnormally porous. In the osteoclastic phase, the bones become very friable and even the shafts assume a spongy appearance. They diminish in density. These changes correspond to the stages of eccentric rarefying ostitis and osteoporosis of German authors. The flat bones often show well-marked periostitis, but the great thickening sometimes seen in certain of the bones of the head appears to be the result of a special osteo-periostitis. It is quite certain that the disease is due to something more than a mere want of mineral constituents in the bone, and poverty in this respect certainly does not explain the hypertrophic changes. The nutrition of the bones as a whole is disturbed, resulting in alterations both in the ossein and in the mineral salts, the whole process being accompanied by symptoms of osteo-periostitis. [Illustration: $1] The fractures which occur so frequently during the osteoclastic phase have well-marked peculiarities. The extravasation of blood is trifling, and no callus forms, even when the ends of the bones are immobilised by external aid; if the ends are left free, they soon become worn and polished by rubbing against one another. In the neighbourhood of the articulations and ligamentous insertions the periosteum soon undergoes change, and it is not uncommon to find sub-periosteal and intra-osseous extravasations of blood. Germain has also noted in horses the disappearance of the intervertebral and articular cartilages, and the frequent occurrence of anchylosis, true or false.