By these terms is meant the pathological deposition of lime-salts. In Ossification we have the salts of lime united with an organic matrix, and the tissue has a definite structure in which living, active cells are present. In Calcareous infiltration the same salts, chiefly the carbonate and phosphate of lime, are deposited in tissues without entering into any proper union with them, and, in fact, the deposition of the lime is in itself evidence that the tissue has virtually lost its vitality. A Concretion is a solid body, formed generally by deposition from a fluid. Such solid bodies consist in many cases of lime-salts.
Lime-salts or other soluble matters may be deposited because they are present in excess. In cases of rapid destruction of bone, as by an advancing cancer, the absorbed lime-salts are present in the blood in excess, and we may have a metastatic calcification of the lung or intestine. There may be thus an incrustation such as to make the tissue like pumice-stone. In some cases of this kind there has been a co-existent disease of the kidneys hindering the due excretion of the lime-salts.
In most instances, however, the presence of dead or obsolete matter or a foreign body is the chief determining cause of deposition. The blood and principal fluids contain lime-salts in solution, and, under certain circumstances, these are liable to precipitation. In the living tissues there is a continual circulation of the fluids, and these latter do not linger long enough to undergo any serious chemical change.
In dead or obsolete structures, on the other hand, the juices will lie stagnant, and are liable to undergo chemical changes. Both in the case of concretions and infiltrations there is usually a foreign body or piece of dead matter as the centre of deposition. In addition, the circumstances are frequently such as to cause stagnation of the fluid.
The lime-salts are deposited in the first instance in the form of fine globular granules, either in the protoplasm of cells or in the intercellular substance. The structure is as if dusted with refracting granules, and the appearances in many respects resemble those of fatty degeneration. (Fig. 53 a.) As the salts accumulate, the appearance of granules is somewhat lost and a more continuous petrifaction results. (Fig. 53 6.) Sometimes the structure becomes in consequence homogeneous and somewhat translucent, as in Fig. 54. The addition of a dilute mineral acid causes the salts to dissolve, and, as carbonates are nearly always present, solution occurs with evolution of gas.
Fig. 64. - Calcareous infiltration of the middle coat in an artery. The lime salts have aggregated together so as to produce a crystalline appearance, x 22.
Examples of this process are very numerous. A minute parasite, the trichina spiralis, occurs in the embryo form in the muscle of man and animals; it lies there quiescent, coiled up spirally and surrounded by a capsule. It is virtually a foreign body, and the capsule is by degrees impregnated with lime, assuming an opaque appearance at its poles (Fig. 55). If the embryo itself dies, it also may become impregnated with lime (see Fig. 55, lower part). Sometimes an extra-uterine foetus dies and remains inside the abdomen as a foreign body. It becomes surrounded by adhesions and partially encapsuled. The capsule and superficial parts of the foetus become through time encrusted with lime, forming the so-called Lithopaedion. Again, an inflammatory exudation in the pericardium may dry in and become impregnated with lime. In phthisis pulmonalis, if healing occurs, the contents of cavities and caseous matter may dry in and become surrounded by a capsule; impregnation with lime results, leading to a pultaceous or mortary material, which may ultimately condense into a stony mass. Again, in valvular disease of the heart, due to chronic endocarditis, the new-formed connective tissue, by its contraction, becomes hard and dry and virtually obsolete, and deposition of lime-salts occurs.
Fig. 55. - Trichina spiralis in muscle. The capsules infiltrated with lime, and in one case a dead worn shrivelled and impregnated with lime.
These are examples of calcification of foreign bodies of pathological products, but we may have the process occurring in the ordinary tissues when they have become obsolete. In the middle coat of arteries of old people, calcareous infiltration, beginning in the muscular fibre-cells, frequently leads to massive petrifaction of the arteries (see Fig. 54), so that they form rigid tubes. The cartilages of old people are also liable to impregnation with lime. The crystalline lens of the eye may be the seat of a similar deposition in certain forms of cataract.
In some cases the calcification is followed by a true ossification. Calcareous infiltration of the middle coat of arteries is not infrequently associated with ossification (Paul, Coats), and the calcification of the ribs of old people frequently passes into ossification. Again, the author found in an old hydatid cyst in the liver true bone associated with calcification. In these cases the rigid calcified structure probably acts as a foreign body, inducing the formation of granulation tissue around it. The granulation tissue may eat into the calcareous mass, and it looks as if the presence of lime-salts induced it to develop into bone rather than into ordinary connective tissue.
Weber, Virch. Arch., vol. vi.; Virchow, do., vols, viii., xi., xx.; Zahn, do., vol. lxii.; Kyber, do., vol. lxxxi.; Paul, Path. Soc. trans., vol., xxxyii., p. 216; Coats, Glas. Med. Jour., vol. xxvii., 1887, p. 265; Cohn., Virch. Arch., vol. cvi.