SPONTANEOUS NEOPLASMS IN MICE 213 



general emaciation accompanied by weakness and kyphosis. The abdomen 

 becomes greatly distended by either enlargement of the spleen or ascites, or a 

 combination of these two conditions. In some advanced cases marked 

 subcutaneous edema obscures the emaciation. When the body cavity is 

 opened, the edematous subcutaneous tissue is found to contain a clear 

 serous-like fluid, and the intra-abdominal liquid may be serous or sero- 

 sanguineous. Hydrothorax is also a fairly common finding when ascites is 

 marked. 



Lymph nodes are not uniformly enlarged. The mesenteric lymph node 

 is usually but not always involved, and may be enlarged to three centimeters 

 in length. Sometimes the spleen is enormous, light gray, friable and granu- 

 lar. Other lymph nodes may be enlarged in varying degrees. In a condi- 

 tion that is generalized the subcutaneous, mediastinal and intraperitoneal 

 lymph nodes are enlarged and tumor cells from them show infiltrations into 

 adjacent normal tissues and organs. The organs outside the lymphatic 

 system which most frequently show gross involvement and tumor nodules 

 are the liver, kidneys and the lungs. 



The microscopic picture presented by these neoplasms is varied, since the 

 tumors may be made up of cells which are predominantly from the unre- 

 stricted proliferation of lymphocytes, of immature myelocytes or of mono- 

 cytes. These cells produce tumors with var\dng frequency in different 

 stocks of mice. Numerous workers have published on this group of tumors 

 in mice. Probably the earliest report was by Eberth (1878). However, 

 many early reports were on small numbers of animals and the terminology 

 employed has sometimes been confusing. More recently there have been 

 several reports employing large numbers of mice and a fairly clear classifica- 

 tion is in use. Tumors resulting from the unrestricted proliferation of 

 lymphocytes and immature myeloid cells are well understood (Table i). 

 The third group, however, is less understood. This is largely because the 

 origin and nature of monocytes are among the most debated problems of 

 morphologic hematolog>\ The interpretation used here is based upon the 

 classification of human tissues employed in the Lymphatic Tumor Division 

 of the American Registry of Pathology (6). From a review of the literature 

 and from experiments conducted by himself and his co-workers, J. Furth 

 (15) gives his conclusions on terminology and says: "that monocytes, 

 histiocytes, macrophages, clasmatocytes, polyblasts, Kupffer cells and 

 microglia cells are synonymous terms for one cell type, which is capable of 

 perpetuating itself by mitotic division. In this (Furth's) communication 

 we shall refer to the round forms of this type of cell seen in the circulating 



