CANCEROUS TUMORS. 7 



only apparently a separate existence, and that everywhere the 

 cancer cylinders stand in direct anatomical connection either 

 ■with the principal cancerous growth, or, at its margins, with 

 the sebaceous glands or the rete-raalpighii. 



It is true that a certain amount of cell multiplication takes 

 place in the connective tissue between the cancer cylinders. 

 It is also true that in man}^ cases the papilloa of the skin elon- 

 gate, branch, and form a prominent framework for the luxuri- 

 ant epithelial growth which takes place upon their surface. 

 But these morbid processes in the connective tissue are to be 

 regarded as quite subordinate to the proliferation of the deeper 

 epithelial layers which produces the cancer cylinders ; and it 

 must be remarked that while the elements of the cancer cylin- 

 ders have all the epithelial characteristics which might be 

 expected from their origin, the progeny of the connective tis- 

 sue corpuscles is a small-celled brood not unlike what is to be 

 observed in ordinary granulation tissue. 



Thiersch supported his interpretation of the appearances 

 shown in his sections by an appeal to the history of the devel- 

 opment of the embr^-o. The first significant fact after the 

 primitive segmentation of the ovule is the differentiation of 

 that part of the surface of the sphere which cori-esi^onds to the 

 future body of the embryo into three distinct layers, a snpcrior, 

 middle and inferior laj^er. Now as the history of development 

 shows that the epithelium of the skin and of all its glands is 

 derived by direct growth exclusivel}' from the superior or horny 

 embryonic layer, while the connective tissue is derived exclu- 

 sively from the middle layer, the idea of the origin of the 

 epithelial elements of skin cancers from connective tissue 

 appears so contrary to the laws of normal development that it 

 ought not to be accepted without the most convincing proof. 



Such, in brief outline, were the views of Thiersch. I com- 

 mend his work to you as a most careful and conscientious stud}'. 

 Whatever may be thought of his doctrine, his book is full of 



