At this period of life, the calcareous substance predominates so much in the economy, that it is thrown upon different organs, such as the arteries, the cartilages, the tendons, which then take the osseous character. We might say that by accumulating in our parts this substance foreign to life, nature wishes to prepare them insensibly for death. In general, it is those organs whose nutritive substance is gelatine, which have the greatest tendency to be placed in relation with the calcareous substance, and consequently to be encrusted with it. Hence why the cartilages especially are ossified; why those of the sutures disappearing, the bones of the cranium become continuous; why the larynx is finally almost all osseous; why the cartilages of the ribs are often as solid as the ribs themselves; why oftentimes many vertebræ united form a more or less considerable continuous mass. I would observe however that the arteries, which have so great a tendency to ossification, are not so evidently gelatinous as many other substances which ossify much less easily, as the tendons for example. III. _Peculiar Phenomena of the Development of the Callus._ Nothing is easier after what has been said upon the osseous nutrition, than to understand the formation of the callus. We know that it has three periods, 1st, the development of the fleshy granulations; 2d, their change into cartilage; 3d, the change of this cartilage into bone. This triple phenomenon takes place in a space of time that varies according to the age, the fracture, the kind of bone, &c. but which is in general longer than that of the other cicatrices. The development of fleshy granulations is a phenomenon common to every species of organ which has experienced a solution of continuity and whose divided edges are not in immediate contact. Here these granulations arise from every part of the divided surface, from the periosteum, the compact texture and that of the cells, the last especially. Those of one side unite to those of the opposite. Thus far the osseous cicatrix does not differ from that of the other parts. This state corresponds with the mucous state of natural ossification. As the fleshy fibres are but the extension of the nutritive parenchyma, they have its vital forces; their organic sensibility follows the same laws as in ordinary nutrition; at first it is in relation with gelatine; this is then exhaled; then commences the cartilaginous state; then the osseous cicatrix takes a peculiar character, which distinguishes it from that of the other organs. At the end of a longer time, the organic sensibility increases in the parenchyma of cicatrization which the fleshy granulations form; then these become in relation with the calcareous substance which comes to the bone, and which they had until then repelled; they admit it then, as well as the red portion of the blood which always precedes it in every species of ossification.