b THE TONER LECTURES. 



marks an epoch in the progress of our pathological views as 

 important as the appearance of the Cellular Pathology. 



Two years before the publication of that paper Professor 

 Carl Thiersch, of Erlangen, published in Leipzig a book on 

 epithelial cancer,* whicli is the first of the more recent special 

 studies to which I wish to invite j'our attention. Thiersch 

 investigated particularly cancers of the skin. He cut great 

 numbers of thin sections and used methods of research which 

 are still extensively employed in the investigation of morbid 

 growths. His general conclusion was quite adverse to the 

 doctrine of Virchow that cancers originate by the multiplica- 

 tion of the connective tissue corpuscles. So far from this 

 being the case, in cancers of the skin at least, Thiersch de- 

 clares that the essence of the morbid process is a cell multi- 

 plication in the lower soft layers of the epidermis, and in the 

 epithelium of the glandular appendages of the skin, especially 

 the sebaceous follicles. The result of this cell multiplication is 

 the production of cylindrical processes, composed of epithelial 

 cells, and growing into the adjacent connective tissue which 

 disappears before them, precisely as happens during the devel- 

 opment of hair sacs and sebaceous glands in the fcEtus. 



These cancer cylinders branch continually as they grow and 

 increase at the same time in thickness, so that their actual re- 

 lations are not easily detected in the older parts of the growth. 

 At the mai'gins, on the other hand, single small slices, such as 

 are usually made for microscopical examination, are apt to dis- 

 play numerous transverse or oblique sections of individual can- 

 cer cylinders, which have been erroneously interpreted as out- 

 lying independent foci, and supposed to originate from the 

 corpuscles of the connective tissue in which they are embedded. 

 If, on the contrary, large sections are made, and especially if a 

 number of thin sections, taken one after another, are compared 

 together, it is easy to recognize that such outlying foci have 



* Der Epitheliulkrebs. Leipzig, 18Ga. 



