336 Tumors. 



The explanatory theories of Cohnheim and Ribbert based 

 upon considerations of embryology and mechanical conditions for 

 growth are far more simple. Tumors have been repeatedly met 

 in the new born ; for example a melano-sarcoma in a calf, a 

 papilloma in a foal, and a number of growths, which although 

 first noted in young animals were of a composition necessitating 

 an embryonal origin for their development, as dermoid cysts, 

 dental teratomata, branchial cleft teratomata. In the earliest 

 stages of embryonic development w^hen in a great variety of ways 

 there occur formation of folds and of buds, pressure displace- 

 ments and separations of the cells growing with unequal rapidity, 

 it is possible that cells and groups of cells may be cut off from 

 the rest, misplaced or isolated. Such misplaced cells will for 

 the most part perish, because of the necessarily occurring nutri- 

 tive disturbances ; but where according to circumstances the 

 nutrition remains sufficient the misplaced cells will continue to 

 grow and multiply, and there is necessaril\' produced from them 

 a structure which is apparently a foreign growth and not nor- 

 mally belonging to the structure of the tissues and organs. The 

 formation of blood vessels probably proceeds in a more or less 

 atypical manner in such separated and misplaced groups of cells. 

 as a result of which their growth is in one instance a very slow 

 one, in another an exuberant cellular proliferation. The experi- 

 mental studies of Roux have shown that by artificial isolation 

 and misplacement of segmentation cells each one is capable of 

 growing into an embryo; and Barfurth has observed that after 

 needling an ^gg in the gastrula stage tumor-like formations 

 (dern^oid-like) develop from the misplaced cells. J^Ioreover Rib- 

 bert has succeeded, by transplantation of fragments of the auricle 

 of a rabbit, in obtaining polypoid nodules persisting for more 

 than a year, consisting of skin, fibrous tissue,- cartilage and 

 bone ; and in other experiments tumor-like structures from bits 

 of the notochord, by transplantation to the anterior surface of the 

 intervertebral tissues. Occasionally the accidental or intentional 

 operative transplantation of epithelium or bits of skin into a 

 wound has resulted in the formation of a small epithelial cyst or 

 dermoid cyst from the engrafted tissue, which may be regarded 

 as evidence in the same line with the larger congenital growths 

 of this type. The fact that experiments of this sort have thus far 

 failed to produce larger tumors of progressiva and persistent 

 character of growth is not an argument against this theory ; we 

 must remember, as Ribbert insists, that our technique in artificial 



