268 THE EVOLUTION OF CONTINUITY 



been considered ; that is, there is a more gradual assumption 

 of tumour characters. And our suggestion is that a tem- 

 porary release from Natural Arrest gradually becomes a 

 permanent and uncontrolled release. 



It is common knowledge that a large number of tumours 

 arise in situations where chronic irritation, inflammation, 

 or ulceration has obtained for some time, and where there 

 are no reasons for supposing that any unnaturally arrested 

 cells have been lying dormant. These tumours are invariably 

 malignant in nature, and chiefly arise in epithelial tissue ; 

 this, no doubt, being largely due to the fact that surfaces 

 exposed to chronic irritation are always covered by one 

 or more layers of epithelium. And in this connection it 

 is necessary to recall what happens in the healing of wounds 

 and the regeneration of tissue. 



With the destruction of a localised area of mature tissue, 

 or on its wounding or severance, the exposed cells are 

 released from arrest and multiply until the tissue loss is 

 made good and local tissue-balance regained. If the wound 

 be clean, and the edges can be brought in close apposition, 

 release from arrest is shown at a minimum and the wound 

 heals by " first intention." But where damage or loss of 

 substance is great, rapid healing is impossible, and tissue 

 restoration requires a considerable and sustained exhibition 

 of release from arrest. In such a case it is chiefly the cells 

 of the connective tissue which by multiplying heal the 

 wound, and this is said to heal by " granulation." The 

 so-called granulation tissue is composed of newly formed 

 cells, at first embryonic in character, but later assuming 

 a spindle shape and largely conforming to the ordinary 

 connective tissue cell-type. It is also rich in newly formed 

 bloodvessels, but contains no nerves. 



When healing by granulation proceeds normally, as 

 soon as the granulation tissue has restored the loss or filled 

 the gap the surface epithelium grows across, continuity is 

 complete, and arrest again obtains. But when the wound 

 is unhealthy or septic, or when healing is prevented by the 

 continued action of an irritating agency, two things may 

 happen : (a) unhealthy granulations are produced in excess, 

 so that the marginal epithelium is prevented from growing 

 across, or is destroyed in its attempts to do so ; or (6) hardly 



