TUMORS OF DOMESTIC ANIMALS 21 
6how caseation and calcification in the later stages, and upon micro- 
scopic examination show the presence of tubercle bacilli. In cattle 
there may be a tendency to excessive hyperplasia of the lymphoid 
structures without the presence of recognizable tubercle bacilli. The 
name of paratuberculous lymphadenitis has been applied to this con- 
dition by some observers. 
Enlargements of lymph glands in hog cholera should not be over- 
looked, but the lesions in the skin, kidneys, and digestive tract make 
possible a differentiation of these gland enlargements from tubercu- 
lous lymphadenitis. 
Simple or typical lymphoma, described by some writers as hyper- 
plasia of the lymph nodes, constitutes another form of lymph-gland 
enlargement, the etiology of which is still in doubt. The thymus 
gland in calves, hogs, and dogs may be greatly enlarged and become 
confluent. Either a single gland or a group may be affected, and 
the enlarged gland may remain for a considerable time without any 
change. The capsule of the gland becomes thickened. On micro- 
scopic examination the general anatomical division of a normal 
lymphoid node is preserved. The germinal centers are often in- 
creased in size and show hyperplasia. The lymphocytes, although 
morphologically normal, are less densely arranged between the 
stouter connective-tissue trabecular. 
LEUKEMIC LYMPHOMA 
Leukemic lymphomas may be acute or chronic in character. The 
acute forms occur at a younger age, whereas the chronic form is 
invariably found later in life. Microscopically, real lymphatoid 
overgrowth is shown by the overdevelopment of lymphocytes, 
reticulum, and sinuses. An excess of lymphocytes appears in the 
circulating blood. This latter condition facilitates the diagnosis of 
leukemic lymphoma from the other forms of lymphoma. 
PSEUDOLEUKEMIC LYMPHOMA 
Pseudoleukemic lymphoma or pseudoleukemia in animals, or Hodg- 
kin's disease in man, is another type of lymphatic hyperplasia, with 
diffuse widespread enlargement of the lymph nodes "but without the 
increase of leucocytes in the circulating blood. Large numbers of 
lymph nodes may be affected in various regions. The spleen is 
invariably involved, but the bone marrow is not altered, as a rule. 
Later in the disease the liver undergoes enlargement and the kidney 
may also become affected. Histologically the enlarged lymph gland 
shows no infiltration. The hyperplasia is due essentially to the over- 
growth of the connective-tissue reticulum, marked prominence of the 
endothelial cells, and an actual reduction of the lymphocytes and the 
cells of the germ centers. There may be an abundance of eosino- 
philes. Increase of connective tissue in the capsule, trabecule, and 
reticulum of the pulp becomes the marked feature, particularly in 
the spleen. 
SARCOMA 
Definition. — Sarcomas are richly cellular, malignant neoplasms of 
connective-tissue origin. The cells are imperfectly differentiated or 
embryonic in type, with a scanty amount of intercellular substance 
