TUMOES. 



491 



Psammoma is the term applied by Virehow to a class of tumors character- 

 ized by the presence of peculiar corpuscles, which usually exhibit a distinct 

 concentric striation, or appear as nodular or rod-like masses. Virehow main- 

 tains that these tumors may be either homologous (benign) or heterologous 

 (malignant) i. e., represent transitions into sarcoma. Virehow proposes to 

 call the corpuscles arenoid that is, sand-like ; they are a normal feature in 

 the anterior portion of the glandula pinealis, where they form the acervulus 

 cerebri. Besides, they are met with in the cerebral and spinal dura mater, 

 especially in the Pacchionian bodies, and in the arachnoid. They are amy- 

 laceous corpuscles, infiltrated with lime-salts, although Virehow insists upon 

 their being different from the corpora amylacea on account of the blue stain 

 of the latter, shown when treated with iodine. Such corpuscles were found 

 also in enlarged hyperplastic lymph-ganglia. The tumors containing them 

 occur both in the brain-tissue and in its investing membranes, especially the 

 dura mater, in the optic nerve and its investments, and in the retina. (See 

 Fig. 190.) 



FIG. 189. COMPACT OR EBURNEAL OSTEOMA, FROM THE FRONTAL 

 BONE OF A MAN. 



L, lamellate*! bone-tissue, pierced by medullary spaces, M, which toward the periphery of 

 the tumor are large and contain several blood-vessels ; while in the more central portions of 

 the tumor the medullary spaces are reduced to irregular Haversian canals. Magnified 100 

 diameters. 



The term "psammoma," applied to a tumor, is obviously superfluous, for 

 the arenoid corpuscles do not determine the nature of the tumor, which may 

 be a myxoma, a fibroma, an angioma, or a myeloma, consequently widely dif- 

 fering in pathological features. The arenoid corpuscles are secondary and 

 incidental formations in these tumors. The same holds good for pig- 

 mented tumors, which occur in rare cases in the pia mater, and are termed 



