THE HABIT OF GROWTH 299 



general. Thus it is that I am led to favour a theory which I 

 believe is applicable to all tumours, whatever their origin. 

 Briefly, this theory is based on the fact that cells and their 

 descendants which for long periods have been subjected to certain 

 influences, whereby their properties and structures have become 

 modified, eventually retain those properties after the influences 

 referred to have ceased to act upon them. I base it again upon 

 that principle of inertia already indicated a principle which 

 some years ago (1896) in this connexion I referred to as the 

 " habit of growth." 1 



Here let me cite certain examples illustrating the existence 

 of this principle in connexion with tumours : 



It is a familiar fact that a columnar-celled epithelium, sub- 

 jected to altered conditions of certain orders, is liable to become 

 converted into a squamous, many-layered epithelium. Such 

 transformation is often noted in the uterus that has been prolapsed 

 and everted ; it has been noted in the gall-bladder after chronic 

 inflammation, and again in the larynx. What is more and 

 this is a point to which I would especially call your attention 

 from the uterine mucosa under these conditions, it has been 

 observed that if cancer develops, it tends not to be of the columnar 

 or adeno-carcinomatous type usual in the uterus, but to be 

 definitely epitheliomatous and of the squamous - celled type. 

 The development of primary epithelioma has been more than 

 once recorded in the gall-bladder, and, as there is no squamous 

 epithelium anywhere in the neighbourhood of the normal gall- 

 bladder, the generally accepted conclusion is that there has been 

 a pre-existing chronic inflammatory condition, which has caused 

 metaplasia of the columnar - celled mucosa into a stratified 

 epithelium. So also where an epithelioma arises in the larynx, 

 away from regions where as along the edge of the vocal cords 

 such stratified epithelium is normally present, the most satis- 

 factory conclusion is that a similar metaplasia has preceded the 

 cancerous development. 



Now certainly in the first of these cases, and most probably 

 in the others, long-continued irritation and modified conditions 

 of environment have led to a change in structure, and this 

 change has impressed itself upon the affected cells to such an 



1 Adami, " The Habit of Growth," Montreal Medical Journal, xxiv., 1896, 

 581. 



