2l6 



BIOLOGY OF THE LABORATORY MOUSE 



less generalized. In the generalized type there is usually a focus of greatest 

 lymph node enlargement. 



Lymphosarcoma. — (Lymphoblastoma sarcoma type.) This type may be 

 leukemic or aleukemic. The cells are more pleomorphic than in lympho- 

 cytoma, showing atypical lymphocytes with irregular nuclei and little cyto- 

 plasm. The more atypical the cells the more malignant the tumor. Mitoses 

 are abundant. 



Lymphocyte tumor cells Mitoses Normal lymphocytes 



I 





'^^^^^^^ 







Fig. 117. — Lymphocytoma in the mesenteric lymph node (X400). 

 Myeloid Cell Tumors 



Only those tumors from myeloid cells which form the granular leukocytes 

 will be considered. These tumors are rare in most stocks of mice, but 

 Barnes and Sisman report that several cases have been seen in their stock Rf 

 and in stock S, and the same is true of Strong's F strain (3, t,^)- The sites 

 of early involvement are bone marrow, the red pulp of the spleen and the 

 medullary tissue of the lymph nodes. Lymph nodes are sometimes greenish 

 (chloroma). In the spleen and lymph nodes the immature myeloid cells 

 surround the germinal centers and may obliterate them. The following 

 criteria have been suggested as an aid in distinguishing between myeloid cell 

 tumors and non-malignant extramedullary myelopoiesis in mice (3). 



