22 BULLETIN 1449, U. S. DEPARTMENT OF AGRICULTURE 
between them. Sarcomas occur frequently in man and in all domestic 
animals. 
Appearance. — Sarcomas are variable in size, shape, color, and con- 
sistence. They may be circumscribed or nodular, but more frequently 
they are diffuse and infiltrate the surrounding tissue. When grow- 
ing near the surface they may finally protrude from the surface as 
red, granular masses resembling exuberant granulation tissue of heal- 
ing wounds. This appearance, resembling flesh, led the older observ- 
ers to name such neoplasms sarcomas, from the Greek word " sarko," 
fleshlike. The consistence of sarcomas depends partly on the shape 
of the cells and partly on the presence of the intercellular substance. 
This is particularly true when fibrous tissue, cartilage, and bone 
enter into combination with the neoplasm. The compactness or close- 
ness of the cell arrangement and the vascularity influence not only 
the softness and the density but have a direct bearing on the color 
found in different types of sarcomas, which will be described later. 
The dark-brown to black color of certain sarcomas is due to the 
presence of melanin, which is a pigment derived from cell metab- 
olism. With the exception of the giant-cell sarcomas, which are 
partly encapsulated, primary sarcomas, as a rule, are not encapsu- 
lated. Secondary sarcomas are more circumscribed and frequently 
show at least an attempt to form a capsule around the secondary 
nodule. 
Seats. — Sarcomas always start from preexisting connective tissue of 
the body. The skin and the subcutaneous tissue, also the intermuscu- 
lar tissue, fascias, the sheaths of tendons, the periosteum of bones, the 
perichondrium of cartilage, and the bone marrow, are among the 
most common seats for their growth. Less frequently sarcomas are 
found in the subcutaneous connective tissue of the respiratory system 
and of the reproductive and urinary organs, also in the serous mem- 
branes of the pleural and peritoneal cavities, in the membranes 
and the nerve tissue proper of the brain and cord or in the support- 
ing tissue, or in the adventitia of the blood vessels of the choroid 
plexus. In the liver, pancreas, lung, and heart, they may appear, 
but usually by metastasis. 
Structure. — Sarcomas retain the cellular structure and undifferen- 
tiated type throughout their growth. The cells of sarcomas vary in 
shape, being round, spindle shaped, or polymorphous in form. There 
is usually a scanty amount of intercellular substance. Their nuclei 
are large, leaving but little cytoplasm around the periphery. In 
rapidly growing forms the nuclei are hyperchromatic, stain well 
with nuclear dyes, and appear granulated or vacuolated, but they 
stain poorly after degenerative changes have set in. With proper 
fixation karyokinetic figures may be seen in spite of the small size of 
the cells. In most sarcomas the intercellular substance is scarcely 
appreciable, but it may become sufficiently pronounced in some vari- 
eties to form well-defined bands of the stroma, which separate the 
cells into groups or columns, forming an alveolar appearance. 
Sarcomas have a different blood supply from other neoplasms. 
The walls of their blood vessels are imperfectly formed and consist 
of scarcely more than a single layer of endothelial cells, and in some 
instances of mere clefts in the sarcomatous tissue through which the 
blood flows. The thin walls in sarcomas favor frequent hemorrhages 
and the detachment of sarcoma cells into the blood current to form 
