CHAPTER 2: 
TUMOURS AND CANCERS. 
TUMOURS are very interesting to the evolutionist, and in 
order to obtain a clear notion of them it will be necessary 
to classify the various “swellings” to which the term is 
applied, and this is more essential as even medical men 
use the word in a very indefinite sense. The term 
“tumour,” which literally signifies “a swelling,” com- 
prises Cysts, Infective Tumours, Sarcomata, Neoplasms, 
and Cancers. Each requires separate consideration. 
CystTs.—A cyst is a tumour containing fluid or semt- 
fluid contents resulting from the dilatation of a pre-existing 
cavity. 
Tumours conforming to this definition arise in different 
ways. For instance, many organs such as the kidneys, 
liver, salivary glands, and the like, are furnished with a 
duct, or series of ducts, whereby the fluid secreted by 
them is conveniently discharged. If from any cause the 
fluid be prevented from escaping after it has been, 
secreted, it will distend the ducts until they become 
dilated into large reservoirs, or retention-cysts, as they | 
are termed. This is well illustrated in the case of 
the kidneys represented in fig. 116. The drawing 
shows the kidneys with their ducts (ureters) and the 
urinary bladder of a terrier. The bladder contains two: 
