TUMORS OF DOMESTIC ANIMALS 33 
The stroma of the cylindrical epithelioma is more loosely ar- 
ranged and is more cellular than the stroma of squamous epithe- 
lioma. The looseness is due to the anatomical differences in the 
structure of the submucosa in which cylindrical epithelioma de- 
velops, from the denser and more compact derm of the skin which 
gives rise to the stroma of squamous epithelioma. Cylindrical 
epithelioma metastasizes slowly, and the secondary metastatic nod- 
ules in internal organs reproduce the columnar type of the parent 
structure. In malignancy and metastasis the cylindrical epithe- 
lioma resembles more closely the glandular carcinoma than the 
squamous epithelioma. 
GLANDULAR CARCINOMA 
Definition. — Glandular or medullary cancers are malignant, meta- 
static, epithelial neoplasms which resemble racemose glands in ar- 
rangement. They are the most malignant and most widely distrib- 
uted variety of cancers in humans and in domestic animals. Sta- 
tistics show cancer to be on the increase, not only in man, but also 
in domestic animals. 
Nature and structure. — Medullary cancers, like surface carcinomas, 
consist of an epithelial parenchyma and a connective-tissue stroma 
or matrix. The parenchyma of glandular cancers forms continuous 
branching cylindrical masses of proliferating epithelial cells which 
extend in various planes. These masses in sections appear as 
alveolar spaces filled with epithelium obliterating the lumen, pro- 
liferating into the surrounding tissue. The cells in cancers differ 
in shape, size, and structure, depending on the kind of gland from 
which the} 7 originated, the pressure exerted by the stroma, and the 
amount of nutrition which the cells receive. These structural dif- 
ferences are sufficient reason why a single cell isolated from a cancer 
does not convey characteristics enough to identify it as a cancer cell. 
In fact that cell could have come from a papilloma, an adenoma, or 
a normal racemose gland. 
The alveolar walls are composed of connective tissue which sup- 
ports the blood vessels and lymph vessels to supply the nutrition to 
the neoplasms. The fibrous-tissue stroma may be scanty or abun- 
dant. When the stroma is scanty the parenchyma forms large 
cancer nests; the neoplasm is soft to the touch and is generally 
known as encephaloid, medullary, or soft cancer. If the stroma is 
abundant and the connective tissue densely arranged the cancer is 
hard to the touch and is known as scirrhous or hard cancer. The 
cancer nests in the hard cancer are small, indicating that the epi- 
thelial cell proliferation is very inactive. Soft cancer develops in 
well-nourished subjects, whereas hard cancer grows in emaciated 
subjects. 
The rapidity of the growth of cancers appears to be influenced by 
the state of nutrition which governs the specific " tissue reaction.*' 
Soft cancers grow more rapidly, as the tissue reaction is diminished 
in consequence of a smaller amount of connective-tissue stroma pres- 
ent, when less resistance is offered to the epithelial-cell proliferation. 
Hard cancer, on the other hand, grows very slowly, as the tissue 
reaction appears to be increased in the emaciated subject where the 
3262°— 26 3 
