362 



HISTOLOGY OF THE MORBID PROCESSES. 



a. SMALL ROUND-CELL SARCOMA. This variety presents the 

 least degree of structural differentiation. The substance of the tumor 

 is composed of small, round cells with single vesicular nuclei enclosed 

 in very little cytoplasm. They are so closely aggregated that 

 they appear to be in contact; but careful examination will often 



reveal a small amount of a nearly 

 homogeneous, finely granular, or 

 slightly fibrillated intercellular 

 substance (Figs. 324 and 325). 

 The tumor is supplied with blood- 

 vessels having very thin walls, 



FIG. 325. 



FIG. 324. 



Small round-cell sarcoma of the neck. 



Fig. 324. Section only moderately magnified, showing- the extremely cellular character of 

 the growth ; the great friability of the tissue is owing to the minimal amount of inter- 

 cellular substance it contains and the intimate relations between the tissue of the tumor 

 and the walls of relatively large, thin-walled bloodvessels. 



Fig. 325. Sketch of a fragment of the tumor, more highly magnified. The cytoplasm around 

 the nuclei is hardly distinguishable, and the cells are separated by only a small amount 

 of an indefinite intercellular substance. 



formed of a single layer of cells, which are usually more protoplasmic 

 than those of fully developed endothelium. These vessels may be 

 very abundant, but, especially if the tumor has been removed by 

 operation, they are likely to be empty and their walls so collapsed 

 that they are not easy of recognition. When seen in longitudinal sec- 

 tion these emptied vessels appear as a double line of elongated, some- 

 what fusiform cells, lying in close contact with the cells of the rest 

 of the tumor. In cross-section they are still more difficult of detec- 

 tion, since the swollen endothelial cells then look very much like 

 the contiguous cells of the growth itself. 



Where the sarcoma is infiltrating the surrounding tissues groups 

 of the round cells, distinguished from the leucocytes which may be 

 present by the character of their nuclei, appear in the interstices of 

 the tissue, the formed elements of which undergo atrophy, either 

 because subjected to increased pressure or because their nutrition 

 is interfered with (Fig. 326). In this way the tumor increases the 



