34 TEE POPULAR SCIENCE MONTHLY 



the nose may follow a disease, ozsena, while in the larynx cancer orig- 

 inates most frequently in the vocal chords which, through their situation 

 and function, are most exposed to various external injurious influences. 



This may suffice to prove the great significance of the continuous 

 action of external stimuli in the production of the majority of the 

 typical cancers of more advanced age. 



While in general we can very well determine the dividing lines be- 

 tween the fields of the typical tumors caused through the action of 

 external stimuli and those due to embryonic disturbances, there may in 

 individual cases be some doubt. A number of pathologists extended it 

 seems unduly the field of the tumors belonging to the latter class. They 

 believed that microscopic studies of early tumors frequently demon- 

 strated that they took their origin not from cells attached in a normal 

 manner to the rest of the organs but from detached small fragments of 

 organs. There would have been good reason to interpret the existence 

 of islands of disconnected cells as an indication of imperfect embryonic 

 development. Careful microscopic investigations show however that 

 in the typical cancers of the stomach and intestines (Hauser, Verse) — 

 with the possible exception of certain atypical so-called carcinoid tumors 

 of the small intestines — and even in the multiple tumors of the skin 

 (Janeway, Loeb and Sweek) the cancers originate through a direct 

 downgrowth of the surface epithelium into the deeper tissues. Condi- 

 tions preceding the development of carcinoma cause primarily an in- 

 creased proliferative power of the epithelium which, as the result of this 

 change, in the large majority of cases grows down into the deeper tissues 

 and destroys them, but in some cases the resistance of the deeper tissues 

 is so great that it successfully counteracts the invasion or dissolving 

 power of the epithelium and the latter may instead of growing down- 

 wards be forced to grow towards the outside of the skin, as we could 

 observe in a case of multiple carcinoma of the skin. This increased 

 proliferative and infiltrative power of the epithelium is therefore the 

 principal characteristic of cancer. 



This change in the proliferative power of the epithelium may be 

 accompanied by a change in the structure of the affected cells, which 

 appear often less differentiated. This loss in the complexity of prolif- 

 erating cancerous cells has been called anaplasia. In other cases, how- 

 ever, this morphological change in the proliferating cells may be entirely 

 absent, as for instance in some beginning Eontgen ray cancers. 



Still furthergoing structural modifications of the proliferating cells 

 may take place in the secondary (metastatic) growths, although on the 

 whole metastases repeat more or less the structure of the primary tumor. 

 Thus we may in the case of a primary carcinoma of the liver find meta- 

 stases in which the tumor cells continue to produce bile just as the 

 normal liver cells do, and especially primary as well as metastatic tumors 



