TUMOES OF DOMESTIC ANIMALS 35 
sither in miliary carcinomatosis of the peritoneal cavity or a general- 
ized deposit of cancer nodules, which are more of the nature of 
plastic masses and frequently become confluent. 
Age as a diagnostic factor. — In human cases the age of the subject 
has considerable diagnostic value, as it has been found that cancer 
usually occurs after middle age, and that malignant neoplasms in 
the young are almost invariably sarcoma. These facts are of great 
interest, as they have some bearing on the frequency of cancers in 
domestic animals. Statistics show that medullary cancers are fairly 
frequent in the glands of aged dogs and mares, whereas in bovines, 
most of which are usually killed at an early age, medullary cancer 
is rare, while sarcomas are more common. Carcinomas are probably 
as frequently found in aged cattle and sheep as in horses. 
COMBINATIONS OF CARCINOMA 
Combinations. — Carcinoma frequently combines with adenoma to 
form adenocarcinoma. This is the most common combination. Opin- 
ions differ as to whether these neoplasms were originally adenomas 
which in the course of growth had proliferation and in which detach- 
ment of the lining cells led to the accumulation of these cells in the 
interior of the acini, resulting in the formation of cancer nests, or 
whether they started as glandular cancer, with a limited number of 
rows of ceils, and as a result of degeneration and accumulation of 
serous fluid the rows of cells separated, resulting in a structure re- 
sembling disorganized acini of glands. 
Vascular changes in carcinomas are frequent, when the neoplasms 
are known as angiocarcinomas or telangiectatic carcinomas. 
Degeneration. — Colloid cancer is often described as a special form 
of cancer. It is more appropriate to call this alteration a gelatinous 
change, as in most cases the entire structure, stroma as well as paren- 
chyma, is changed into a substance resembling jelly, which is in 
reality a retrogressive mucous degeneration. Very rarely a true 
colloid degeneration affects the epithelial parenchyma; when such 
change does occur it is usually in neoplasms of the thyroid gland. 
Cancers of the stomach, mammary gland, and intestines are affected 
more often by mucous degeneration than by colloid. 
Suppuration is very common in all forms of cancer, especially 
when they are exposed to infections of pathogenic microorganisms 
inducing a septic condition in the body. The products of septic 
microorganisms are toxins which are absorbed into the blood stream, 
producing a general disturbance known as cancerous cachexia. 
Infection. — Clinical observations show that cancers of the mam- 
mary glands are invariably sterile unless surface ulceration has set 
in,. which sometimes occurs in advanced stages. Some of the cancers, 
as those of the lip, tongue, esophagus, and especially those of the 
uterus, intestine, and rectum, harbor excessive numbers of micro- 
organisms. Such cancers are usually called infectious cancers. It 
is therefore important to bear in mind that long-protracted, chronic 
Eases of cancer may terminate in death by terminal infection, which 
may result in uremia, pneumonia, meningitis, or peritonitis, and is 
due to the toxins formed by the multiplication of microorganisms 
that infect the cancer. Infectious cancers often resemble chronic 
