484 TUMORS 



due to the large niiml)cr of ])lood vessels they contain, their softness, 

 and very thin epithelial covering. The writer has noticed that dogs 

 affected with condyloma of the vulva or penis also show these formations 

 quite frequently on the edges of the lips. Gratin has often seen the 

 obscure transmission of condylomata from one dog to another. This 

 would tend to establish the fact that this variety of tumor is contagious. 

 (See Infectious Genital Tumors.) 



5. The Carcinoma. — By the term carcinoma we designate that neo- 

 formation the essential feature of which is the overgrowth or accumula- 

 tion of epithelial cells, some of which have penetrated the basement 

 membrane, by root-like projections, into the underlying or neighboring 

 structures. It is the commonest of all neoplasms. These cells possess 

 the peculiar property of forming metastases, by way of the lymph 

 channels, producing a general cancerous infection of the body (carci- 

 nomatosis), and are, therefore, considered malignant. Any organ or 

 structure in the body having epithelium in its make-up may be the seat 

 of carcinoma. Most cancerous forms are distinguished by their tendency 

 to regressive metamorphoses. These include mucoid, colloid and fatty 

 degeneration, with cystic formation, calcification, cicatricial contraction, 

 and in superficial carcinoma of the skin and mucous membranes, ulcer- 

 ative processes, with the formation of purulent foci. Those showing 

 a strong tendency to spread over the surface are termed "phagedenic." 

 Necrotic changes are frecjuent, the ulcerating portions discharging a foul, 

 sometimes bloody, material. In cases of some standing the dog may 

 show the effect of this process, losing flesh and showing a general condition 

 of cachexia. Carcinomata are generally divided into: 



(a) Squamous epithelioma, sciuamous cancer, or cellular epithelioma. 

 This variety occurs in the cutaneous membrane, and in all mucous 



membranes containing squamous epithelium, as the mouth, throat, 

 larynx, eyelids, ears, cheeks, external genitalia, bladder and urethra, 

 rectum, vagina and uterus. This form of cancer is frequently seen in 

 old animals. It is a peculiar fact that this cancerous growth may accu- 

 mulate rapidly for a short time, and then remain stationary without 

 increasing further in size. Squamovis epitheliomata appearing in the 

 mucous membranes, especially the vagina, which deserves special men- 

 tion, have a great tendency to extend superficially, followed by a cancer- 

 ous disintegration, also by a constant, bloody, purulent discharge. 

 Ulceration usually takes place in these cancers, sooner or later. Some 

 parts may be covered with a scab-like crust, while other parts may be 

 raw and bleeding. Fistula:' frequently form. 



(b) Adeno-carcinoma, or malignant adenoma. 



This variety may originate in any organ containing glandular 

 epithelium. It is probably most often seen in the mammary glands of 



