Actinomycosis.
—The general character of this parasitic disease has already been considered. (See [Chapter VIII].)
The peculiar fungus may be found in the periosteum, in the compact outer layers of the bone, or within its more spongy depths. When the lesion is sufficiently large to be recognizable to the naked eye it assumes, for all practical purposes, the appearance of caries, like that due to tuberculous or leprous diseases, while in the pus or debris discharged from the same or contained within the invaded bones the characteristic yellow, cheesy, or calcareous particles will always be recognized. In this disease there never seems to be the slightest tendency to encapsulation nor to protect against further spreading by any process of repair. The diseased area constantly enlarges its dimensions, involving everything as it spreads, it being limited by no membrane or tissue of the body. Occurring in the bones, it is usually a secondary or metastatic infection, and may be found in any part of the body.
The symptoms will be those of osteoperiostitis, first occurring frequently in the jaws, as it nearly always does in cattle, and often in man; this is accompanied by loosening of the teeth and involvement of the submaxillary tissues. The course of the disease is slow, with little or no tendency toward spontaneous recovery.
TROPHONEUROTIC DISEASES OF THE BONES.
Under this heading it is proposed to group a number of diseases whose clinical manifestations are distinct or classic, but whose underlying causes are more or less obscure.
Achondroplasia.
—This is a lesion of intra-uterine life which includes a softening of primary cartilaginous structures and curvature or malformation of the bones which should be formed from them. It belongs to that period of fetal life between the third and sixth months. It is sometimes referred to as intra-uterine rickets. Under this name it was first described by Müller, in 1860, and since then under various names, most commonly as fetal rickets. It appears that in this disease the fetal cartilage contains mucus abnormally collected, quite generally, in minute cavities or cells just at its borders. The chondroblasts and osteoblasts are not regularly dispersed, and the development of the growing bone is thereby much interfered with. The periosteum appears to have nothing to do with this condition. In consequence the cartilage does not do its proper duty. The long bones fail to attain their proper proportionate length, but become thicker than normal, the periosteum being unaltered. On the other hand, those bones into whose formation cartilage enters but slightly, such as the clavicle and the ribs, retain their normal proportions—the consequence is a peculiar malformation and disproportion of the whole skeleton ([Fig. 236]).
These deformities are symmetrical, and pertain mostly to the bones at the base of the skull and to the long bones of the limbs; therefore the distinctive appearance may be recognized even at the birth of the child. The head is disproportionately large, the spinal column short, the lumbar curvature exaggerated, all of which is rather the reverse of the ordinary rachitic manifestations. The disease is not common ([Fig. 237]).
Fig. 237