(B.) CONCRETIONS Or PSEUDO-CALCULI.— Concretions are masses composed of saline materials deposited in a pre-existing organic basis,— the former, as they increase, gradually encroach on and, as it were, dispossess the lat ter, until eventually, in many instances, all ob vious traces of its existence have disappeared. The saline matters are commonly deposited punctatim ; and the organic basis,. in which they accumulate may be non-stromal (as, for example, tuberculous matter, atheromatous matter, Szc.), or stromal (as, for example, fibrous tumour, Sze.) And, again, the natural tVALL11{7,0 101 lellUlal LIbbLle, tendon, &c. in the case of tophaceous con cretions) ; the solid elements of the cir culating fluid (as the fibrin of the blood in the case of phleboliths) ; and, lastly, various adventitious:substances (as those mentioned above), may severally act the part of that organic basis.
(a.) Elementary cell. — Perhaps the sim plest form of true concretion iS that which an epithelium-cell becomes coated -or studded with saline material. We have seen this con dition in the epithelium lining adventitious cysts, in the epithelium floating in pleuritic , effusions, and occasionally in that discharged with the urine. The concretions, not very un commonly found in the choroid plexus, con sist of round cells coated with calcareous salts. Flakes of albuminous substance may some times be seen in the urine coated with saline matters ; but this is merely a rudely analogous condition to those previously mentioned.
(b.) Foetal (petrifactions).—At the opposite extreme to cases in which a simple elementary cell becomes the depositary of calcareous mat ter, stand those remarkable instances in which an entire individual becomes more or less com pletely invested with a coating of such matter ; while subsequent desiccation of the tissues (with, very rarely, partial calcification of these) mummifies the entire frame.
(c.) Placental.—Caleareous concretions are of not uncommon occurrence in the human placenta. Hannover found them in large number in twenty of two hundred placentae.
They are of white colour, rounded or branched in shape, and composed of phosphate of lime ; generally seated on the uterine, rarely on the fcetal, surface, near the border. The age and constitution of the mother or of the child, separation of the placenta, and hwmorrhages, appear to Hannover to be without influence on their production.
(d.) Vascular.—Arteries,—(1.) Parietal.— There are fevv conditions more familiar to the observer than the calcareous deposition in the coats of arteries, long erroneously styled " ossification " of these tubes. The saline materials, giving the ossiforni aspect to the de position, assume four different forms: 1. That of a gritty looking substance sprinkled over the internal surface of the vessel; 2. That of patches of variable size and thickness, some times sufficiently extensive to convert a con siderable tract of the vessel into an inflexible tube ; 3. that of small rounded or shapeless masses, protruding or not into the interior of the vessel ; 4. that of prominent spiculw ; when their anatomical constitution appears more allied than under other circumstances to that of bone.
Mr. Brande found these incrustations to consist of sixty-five and a half per cent: of phosphate of lime and the rest of animal matter. These proportions must of course vary in different cases : thus Scherer * found " ossified " arterial membrane composed of — Organic matter 7.292 Phosphate of Hine 63.636 of magnesia.. 10.909Carbonate of lime 18.181 M. Bizot t has given a tabular view of the relative frequency with vvhich different parts of the aorta become the seat of this condition ; and from this we learn with more precision than could be otherwise attained, that the points at which the different branches are given off are far the mast frequently im plicated ; and that the posterior surface of the thoracic and abdominal divisions of the vessel suffers more frequently than the anterior in the proportion of 11 to 1.