TUMORS. 319 



sheaths around them (Fig. 158 and Fig. 159). The masses of cells thus 

 formed, with a blood vessel for a centre, may be closely packed together 

 in long strings with more or less frequent anastomoses or they may be 

 arranged in rounded groups, giving to the tumor an alveolar appearance 

 (Fig. 160). Such tumors are called angio-sarcomata. Simple vascular- 





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FIG. 160. ANGIO-SARCOMA. ENDOTHELIOMA ? 

 Tumor of lymph-node. 



ity, although this be extreme, does not make of a tumor an angio- 

 sarcoma. 



Alveolar Sarcoma. Sometimes, as above stated, the basement sub- 

 stance of the sarcomata, particularly in some of the round-celled varie- 

 ties, is quite abundant and arranged in a wide^meshed net, in the meshes 

 of which the cells lie. These spaces are called alveoli, and this variety 

 of structure has acquired importance from the general resemblance which 

 these tumors have to the well-defined and characteristic alveolar structure 

 which many of the carcinomata exhibit. It is true that occasionally the 

 resemblance is very close indeed, but usually the sarcomata present a 

 more or less intimate relation between the cells and basement substance. 

 The cells usually do not simply lie in the cavities, but are often attached 

 to the intercellular substance, which not seldom sends finer trabecula3 

 into the alveoli between the cells. Sometimes a careful shaking of sec- 

 tions in water is necessary to reveal the characters of the reticulum. 

 The cells, moreover, are usually, though not always, distinctive in char- 

 acter. This form of tumor is, in some cases at least, determined, as 

 above stated, by the new formation and peculiar arrangement of the 

 blood-vessels. Tumors of this kind are not common, but may occur in 

 the skin, lymph-nodes, bones, and pia mater. They are usually very 

 malignant. Many of these tumors are doubtless more properly classed 

 among the eudotheliomata. 



Mixed Forms of Sarcoma. In addition to the above mqre or less well- 

 defined forms of sarcoma, there exist various modifications which have 

 received special names. The sarcomata in which cysts form, either by 

 the softening of tissue by degeneration, or by the dilatation of gland 

 ducts by pressure, or by the new formation of tissue in gland ducts or 

 alveoli which dilate with the growth of the tumor, have received the 

 name of cysto-sarcomata. 



