84 CYSTS. 
a peculiar translucent material called colloid. It may not be confined 
to the cells, but may partly fill the alveolar spaces of the tumor. 
What is a melano-carcinoma ? 
It is a carcinoma containing granules of a black or brown pigment 
in varying quantities. 
Describe a carcinoma myxomatoides. 
Cysts of different sizes containing a mucous fluid may be formed in a 
carcinoma by means of the mucous softening of the cells. To sucha 
cancer this term is often applied. It should, however, be applied to 
those carcinometa in which the stroma is composed of mucous tissue. 
MIXED TUMORS. 
What are the mixed tumors ? 
They are formed by various combinations of the different types of 
tumors, and in naming them the name of the more important type of 
tumor present is used as the substantive, and that of the less important 
type as the qualifying term. 
What are the teratoma ? 
They are complex, congenital tumors, of different forms of tissue, 
formed most often at the lower end of the spine, about the head and 
neck, and the organs of generation. Some of them probably arise by 
an inclusion of portions of another foetus. 
CYSTS. 
Into what classes may cysts be divided ? 
I. Cysts which develop in pre-existing cavities. 
IL. Cysts which originate independently as the result of pathological 
changes. 
Name and describe those belonging to the first class. 
Retention and exudation cysts. 
The former being formed by the accumulation in glands or excretory 
ducts of the more or less altered secretion of the gland, e. g., comedones, 
ranulze ovula Nabothi, milk cysts, serous cysts of ovaries, Fallopian 
tubes, and uriniferous tubules. 
The serous cysts occur as the result of chronic inflammatory pro- 
cesses in the lymph spaces or serous sacs, e. g., ganglia, hydrocele, ete. 
What cysts may originate from pathological changes ? 
(a) Cysts formed by the softening and disintegration of tissue; 
at first these cysts have no well-defined wal!, but later a definite wall 
