TUMOURS AND CANCERS. 



243 



to dip below the surface and invade the underlying 

 tissues. In their simplest form such downgrowths are 

 at first solid and club-shaped. Subsequently the central 

 cells liquefy whilst the peripheral ones arrange themselves 

 in a definite and regular order, so as to form a lining 

 membrane to the central chamber, or acinus. The por- 

 tion of the acinus near the surface from whence the 

 downgrowth originated is slightly narrowed and consti- 

 tutes the duct of the gland. This is one of the simplest 



FIG. 122. The microscopical appearance of an epithelial 

 Tumour (Cancer). 



forms of gland, and from it any complex type may be 

 derived by buddings or outgrowths from the primary 

 epithelial germ (fig. 122). Secreting glands are arranged 

 by anatomists into groups according to their structure. 

 Physiologists give them specific names according to the 

 secretion furnished, such as mucus, sweat, milk, and the 

 like. Structurally they form two main groups, tubular 

 and racemose. The simple tubular gland is met with in 

 the intestine of man and in any mammals, whilst the 

 racemose variety is represented by sebaceous glands 



