. General surgical pathology and therapeutics, in fifty-one lectures .. . t to Virchows investigations, the pearls of the intracranialtumors are composed of connective-tissue cells; hence they shouldbe classed with sarcomata. Thymus pearls are the physiologicalexamples of this form, which from their non-vascularity also have ananalogy to tubercle. Another tumor described by Virchow and renamed belongs here,the psammona. This also has only been observed in the brain or inthe orbit, and is related to the villous and to plexiform sarcoma,which we shall soon describe. This varie
. General surgical pathology and therapeutics, in fifty-one lectures .. . t to Virchows investigations, the pearls of the intracranialtumors are composed of connective-tissue cells; hence they shouldbe classed with sarcomata. Thymus pearls are the physiologicalexamples of this form, which from their non-vascularity also have ananalogy to tubercle. Another tumor described by Virchow and renamed belongs here,the psammona. This also has only been observed in the brain or inthe orbit, and is related to the villous and to plexiform sarcoma,which we shall soon describe. This variety of tumor is characterizedby the occurrence of calcareous spheres, having the form of the con-crements which are found in the pineal gland, and are there knownas brain-sand (troafjifiog, sand). Like the thymus pearls, these aremostly connected with the vessels, and are probably mostly calcifiedendothelial pearls; but Virchow says that direct calcification ofconnective tissue may lead to the same forms. (h.) Plexiform (cancroid, adenoid) sarcoma. This form of sar- 754. Psammona, after Virchow. Magnified about 200. coma also is chiefly found in the orbit and brain, but sometimes oc-curs in the parotid gland. It can only be distinguished by verycareful examination from some forms of carcinoma to be hereafterdescribed. Plexiform cylinders, clubs, and spheres of small cellsspread out in the connective tissue, separating its bundles and fillingall the interspaces between them, in doing which they naturally pushinto the lymphatic vessels and perivascular lymphatic spaces. Itcannot always be determined whether the cells first increasing arewandering cells, connective-tissue cells, or cells from the walls of thevessels, endothelium, or perithelium ; perhaps they all participate atthe same time or after one another. The cells first proliferated are as a rule small, round, or irregu-larly polygonal; gradually the following often complicated meta-morphoses occur in these cell-cylinders:
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