302 



VETERINARY PATHOLOGY, 



cellular elements, as (1) round-celled sarcomata, (2) spindle- 

 celled sarcoiL'ata, and (o) myeloid-celled sarcomata. 



Round-cell sarcoma. This tumor is composed primarily of 

 round cells (spherical cells) and is rather common. They de- 

 vclny) in any tissue and are, as a rule, the most malignant tu- 

 mors of this entire group. The)' are soft, spongy, and usually 

 (juite vascular, and, as a rule, are not encapsulated. 



Structurally the cells of this variety approximate the embry- 

 onic epithelial cells more closeh- than do those of any of the 

 uther t}'pes. According to the size of the cells two classes may 

 l)e recognized, ^'iz. : small and large. There is, however, no dis- 

 tinct line between the two classes. The small, round cells are 

 about the size of lymphocytes while the large, round cells are 

 as large and sometimes much larger than mrmonuclear leuco- 

 cytes. The nuclei of this type of sarcoma cells are, relatively, 

 much larger than the nuclei of lymphoc3''tes or leucocytes. In 

 fact, the nucleus occupies practicalh^ the entire cell bodv. The 

 intercellular substance is yery limited and is usually mucoid or 

 reticular. Blood vessels are usually numerous, and their walls 

 are fref|uently formed by sarcdmatous cells. Metastatic growths 

 are frequenth- in this type. The cut on page 27?> is from a ph(-i- 

 tograph of the lung of a horse, showing metastatic round-celled 



Fi&'. 158. — Photo.?raph of sheep's heart, showing a lympho sarcoma of the 



pericardiuin. 



