6 BULLETIN 1449, U. S. DEPARTMENT OF AGRICULTURE 
The peripheral cells in malignant neoplasms proliferate more 
rapidly and receive more nourishment from the surrounding tissues 
than the cells in the interior of the neoplasm. Insufficient nutrition 
and increased pressure, to which the inner portion is subjected, bring 
about degenerative changes which are followed by atrophy and ab- 
sorption of the inner portion of the neoplasm, resulting in the forma- 
tion of a cavity. The cavity may contain remnants of the degenerated 
product, or may be filled with an albuminous fluid or serum result- 
ing from negative pressure. 
Marked anemia, emaciation or wasting of the body and extreme 
cachexia are invariably associated with malignant neoplasms (can- 
cers) of the esophagus or the stomach, which interfere with the pas- 
sage of food, resulting in starvation; some malignant neoplasms (sar- 
comas) in other locations, though larger in size, may not produce 
such marked cachexia. 
Superficial malignant neoplasms often ulcerate around their peri- 
phery. The ulceration may be accompanied by inflammatory changes 
and offers a favorable soil for bacterial infection, and inflammation. 
These processes, singly or collectively, may produce soluble sub- 
stances which are absorbed into the circulation and contribute largely 
in bringing about cachexia. 
Chemical analysis of neoplasms has shown that their composition 
closely approximates the composition of the structures from which 
they grow. Glycogen has been found in excess in neoplasms which 
originated in tissues that normally contain glycogen. Enzymes are 
likewise present in greater quantity in certain neoplasms than in the 
normal tissues from which they grow. 
During the last few years pathological chemistry has been actively 
used in research of neoplasms in human-cancer investigations and in 
the transplantation experiments of malignant neoplasms. 
Malignant neoplasms differ in their rapidity of growth, depending 
on the location and the blood supply of the tissue. They also differ 
in the extent of their metastatic ability. Some are more prone to 
metastasis than others, the latter expressing their malignancy by 
peripheral invasion of the surrounding tissues. Recurrence, which 
is the chief feature of malignant neoplasms, is also variable, depend- 
ing on the difference in type. Under exceptional circumstances 
malignant neoplasms have been known to revert or undergo 
apparently spontaneous retrogression, resulting in their complete 
disappearance. 
Degenerative changes in benign as well as in malignant neoplasms 
are very common. Any degeneration that affects an organ or a tissue 
may likewise affect a neoplasm, as albuminous, fatty, mucoid, or 
colloid degeneration. Calcification, pigmentation, glycogenous in- 
filtration, necrotic changes, and hemorrhages may also be observed in 
neoplasms. 
CLASSIFICATION BY STRUCTURE (HISTOGENETIC CLASSIFICATION) 
The histogenetic classification of neoplasms is based on the struc- 
tural elements of which the neoplasms are made up. This classifica- 
tion was suggested by Virchow (21) after the development of the 
cell doctrine and the fact that the animal body is composed of ele- 
