30 BULLETIN 1449, U. S. DEPARTMENT OF AGRICULTURE 
from a process of budding of the preexisting tubules or saccules of 
the gland. Adenomas have no ducts, and any secretion that may 
be formed in the neoplasm remains in the acini, distending the 
alveoli, and forming cystlike dilatations. The neoplasm then is 
known as cyst adenoma. The retained secretion is of a degenerative 
character. In simple adenomas the epithelium rests on the basement 
membrane, as in a normal gland. 
Destructive adenoma. — When the cell proliferation is so active 
that the epithelium has been desquamated, the neoplasm assumes a 
malignant tendency and is known as destructive adenoma, often 
found in uterine neoplasms, or as adenocarcinoma, which is fre- 
quently present in mammary and rectal neoplasms. 
CARCINOMA 
Definition. — Carcinoma or cancer is the type of a malignant epi- 
thelial neoplasm. The name " cancer " is universally used by the laity 
to designate a dreadful affliction in man and a hopeless condition in 
animals. This conclusion is derived from the fact that the num- 
ber of deaths in man annually amounts to tens of thousands. No 
other neoplasm has received from scientists more attention, study, 
painstaking investigation, and special research to ascertain the true 
cause, the mode of propagation and spreading, and means of eradi- 
cation and control. 
Carcinomalike adenomas are epithelial neoplasms of glandular 
origin. Although the individual gland compartments in adenoma 
are tubular or alveolar in structure, with the acini lined by a single 
layer of cells and a lumen in the center of the acini, the epithelial 
cells of carcinoma are heaped up in irregular clumps, nests, or cyl- 
inders, which are continuous with one another. These clusters 
of epithelial cells penetrate the surrounding tissues by budding or 
by an extension of branching processes that have been compared to 
the roots of a tree or the legs of a crab. From this resemblance the 
name " cancer " originated. 
The epithelial cells in cancers are the most conspicuous structures. 
The cells are in different stages of development and vary greatly 
in shape and size. Therefore, the statement sometimes found in 
print that " a typical cancer cell," found in a certain preparation 
or present in a certain neoplasm is diagnostic of cancer, is an errone- 
ous and misleading impression. It is not the size, shape, structure, 
or variety of a cell that determines whether it is a cancer cell, but 
the relation of the parenchyma to the stroma that determines 
whether the epithelial cell and fibrous-tissue combination should be 
called carcinoma, adenoma, or papilloma. 
A single cell isolated from a cancer can not be told with certainty 
from a normal epithelial cell. The epithelium in the cancer is the 
more conspicuous or basic structure, but the interstitial tissue, which 
may be either scanty or excessive, is of great importance in the de- 
velopment of cancers. According to Ribbert, (17) " cancers always 
start from chronically inflamed tissue." 
Chronic inflammation of connective tissue brings about cell pro- 
liferation. The accumulated connective-tissue cells multiply and sep- 
arate the epithelial cells by destroying the intercellular cement. The 
liberated epithelial cells then begin to multiply, acting collectively as 
