270 DISEASES OF DOMESTICATED BIRDS 
form of the growth was sometimes met with. Despite their diversity, 
the tumors graded into one another and in the final analysis, all are 
to be considered as spindle-celled sarcomata. 
Attempts to obtain an action of the etiological agent upon cells 
other than those it usually affects have failed, as have attempts to 
bring about changes in the histology of the sarcomata by attenuating 
the agent. 
Some of the lesser morphological variations in the sarcomata are 
undoubtedly due to local conditions of the host, and of the more im- 
portant changes some have been associated with an increase in the 
malignancy of the growth. For others the determining conditions 
have yet to be discovered. On the whole the variations described are 
not more marked than those occasionally manifested by the trans- 
plantable mammalian tumors, and traceable to the changes in a single 
strain of tumor cells during their propagation in successive hosts. 
In mammals the ultimate reason for these changes is not known. 
In the case of the chicken tumor some of them are undoubtedly the 
expression of changes in the causative agent of the growth. 
Rous and Lange describe a spontaneous chicken sarcoma. The 
subject was a mongrel brown Leghorn hen which was rendered lame 
by swellings on the left leg. The growth regarded as the primary 
one was located in the gizzard. It occupied nearly the whole right 
anterior portion of the organ and projected irregularly under a cover- 
ing of mesentery in which were located several small nodules. The 
mass was roughly spherical and was about 4.3 cm. in diameter. The 
tumor was surrounded by muscle and encroached on the gizzard 
cavity. The tumor had no capsule but was sharply defined by its 
pale pinkish white color as contrasted with the wine color of the 
muscle. The tumor was made up of many irregular, tightly com- 
pressed subdivisions separated by minute, irregular fissures, and, 
bulged on the cut surface. A localized soft yellow area of necrosis 
was located to one side, but in general the growth was translucent 
and appeared sound though poorly vascularized. The liver was en- 
larged, congested and mottled with ill defined, pale areas. Two 
small stellate depressions making irregular gray areas in the paren- 
chyma, were located on the surface of the organs. These proved to 
be composed of tumor tissue. The other viscera appeared normal. 
An oblong smooth mass 4.5 by 3 by 83 em. was located in the ex- 
tensor muscles of the left thigh. A similar one was located in the 
muscles below the knee. The upper mass was attached to the peri-" 
osteum for about 2 cm. above the patella and also to the joint capsule. 
