242 E VOL UT1ON AND DISEASE. 



a large size. Such a tumour of a tree is termed a 

 xyloma. The bud-like character of such woody tumours 

 is shown in an interesting series presented to the 

 museum of the Royal College of Surgeons by Mr. 

 Stephen Paget. From some of the tumours buds have 

 formed, and in one case the bud has grown into a 

 minute branch. Every swelling on a tree, however, is 

 not a woody tumour or xyloma ; many are due to the 

 irritation of insects. 



CANCERS. We have now to consider the tumours 

 whose main structural peculiarity is that they contain 

 epithelium. The group is of great importance in that it 

 includes the terrible disease known as cancer. It is only 

 of late years that the term cancer has come to possess 

 any strictly scientific significance. In the early days of 

 pathological anatomy any tumour presenting malignant 

 characters was termed cancer, but in the present day 

 the term is restricted to tumours structurally resembling 

 imperfectly formed glands. In order to appreciate the 

 nature of cancer it will be advantageous for us to briefly 

 study the evolution of glands in general. I can only 

 attempt to give in abstract the large amount of evidence 

 I have accumulated, in order to show that cancers are 

 aberrant glandular formations, and may not inaptly be 

 defined as " biological weeds." 



In complex animals the free surface of the body and 

 the alimentary canal is covered with cells differing from 

 those found in the underlying tissues. Such cells are 

 known collectively as epithelium, and though varying in 

 shape in different situations and under various conditions, 

 present identifying characters. This epithelium is prone 



