166 The Lymphocyte and Lymphocytic Tissue 



spherical nuclei (Fig. 13-2). These cells are densely packed, often in mitosis, 

 and infiltrate the tissues underlying the epithelium. The resemblance of 

 these cells to malignant lymphoid cells suggested one of its synonymous 

 names, transmissible lymphosarcoma. 



The origin and nature of the cells are still a matter of controversy. Bloom, 

 Paff, and Noback 4 consider them to be mature end cells of reticuloendothe- 

 lial origin; Mulligan-' relates them to histiocytes; Jackson 17 and DeMon- 

 breun and Goodpasture 5 feels that their origin is uncertain but that they are 



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Fig. 13-2. Canine venereal tumor. Individually discrete cells infil- 

 trating dermis, (x 440) (AFIP 710174.) 



most closely related to the lymphocytic series. In addition to being trans- 

 missible, this lesion is generally self-limiting, is confined to the genital 

 system, and confers immunity to further attacks. However, in a few animals 

 metastases and extragenital lesions occur which may or may not be re- 

 lated. 



The extragenital lesion which simulates malignant lymphoma of the skin 

 is histologically indistinguishable from the venereal tumor but is not identi- 

 cal in all clinical aspects. This lesion appears rapidly in young dogs, usually 

 as a single lesion which displaces the dermis and elevates the epidermis. 

 The lesions are circumscribed, usually from 2 to 5 cm. in diameter, and 

 are often ulcerated due to licking or scratching by the afflicted animal. 

 Histologically they are made up of individual round cells which infiltrate 



