HABIT AND METAPLASIA 247 



totally different habit. It may be asked whether here I am 

 using the term in the same sense as previously, whether what I 

 here term habit is not the result of continued alteration of environ- 

 ment. It may be asked whether in these cases return to the 

 normal environment would not bring about return to the normal 

 type of tissue, or whether this altered habit of growth persists. 



To this I would answer that undoubtedly it tends to persist. 

 As evidence I may cite the example of a region in which epithelial 

 metaplasia is not uncommon, namely, the gall-bladder. There, 

 as a result of the chronic irritation set up by the presence of gall- 

 stones, it is not uncommon to find larger or smaller areas of 

 squamous epithelium taking the place of the normal columnar- 

 celled mucosa, and this more particularly in the region of the 

 fundus. Now, as is well known, 90 per cent or more of cases of 

 cancer of the gall-bladder are associated with cholelithiasis, and 

 the majority of those cancers originate in the fundal region ; 

 and the interesting point is that I have encountered (and there 

 are several similar cases recorded in the literature) cases in which 

 that cancer, instead of being of the adenocarcinomatous type 

 which one expects to originate from a columnar-celled epithelium, 

 approximated to the squamous epitheliomatous type. They 

 were not absolutely typical epitheliomas ; epithelial pearls, for 

 example, have been wanting. My own case, for example — and 

 others have made the same observation, — exhibited a mixture 

 of alveolar masses of the epitheliomatous type, along with other 

 alveoli of adenocarcinomatous appearance. But certainly these 

 were not ordinary adenocarcinomas. There is no epithelium in 

 the neighbourhood of the developing gall-bladder of squamous 

 epithelial nature ; no chance, therefore, that these tumours 

 develop from a squamous epithelial cell rest. The only adequate 

 explanation is that the metaplastic squamous epithelium has 

 its characters so firmly impressed upon it that, when it gives 

 rise to a cancer, its cells, as they infiltrate into the surrounding 

 tissues, do not revert to the columnar type, but give rise to a 

 squamous epithelial new-growth. Again an acquired variation 

 becomes hereditarily transmissible among the cells. They have 

 " got the habit." 



Some of you may know that many years ago I applied this 

 habit conception to the elucidation of tumour growth in general, 

 and though in the meantime I have amplified my views, I still 



