TUMOURS AND CANCERS. 241 



grew erratically or aimlessly and formed tumours. This 

 view has been discussed critically by almost all writers 

 on tumours since Cohnheim expressed it, and it un- 

 doubtedly accounts for many neoplasms. The great 

 objection to the view has been that such undeveloped 

 rudiments have not been shown to exist. More careful 

 researches show clearly enough that among the great 

 class of morbid productions generically referred to as 

 tumours, Cohnheim's theory holds good for cysts, many 

 neoplasms, and a remarkable group known as dermoids, 

 and by a careful extension of the definition " tumour 

 germ," it could be applied to cancer. Restricting the 

 application of this theory to the tumours indicated, this 

 view offers adequate explanation of bony and carti- 

 laginous neoplasms, of some vascular tumours, and those 

 which have been already referred to as arising in con- 

 nection with vestigial structures. (See Chapters III. 

 and IV.) 



The full details cannot here be discussed, but any one 

 exercising patience in such anatomical inquiries will 

 soon be able to satisfy himself, as I have done, that 

 " tumour-germs " actually exist in our bodies, and of 

 such a character as Cohnheim's theory requires. The 

 erratic growth of such undeveloped portions of tissue 

 may be well illustrated in a simple way by examples 

 from the vegetable kingdom. The stems of trees and 

 woody plants form a large number of buds, most of 

 which grow into branches. Some of these remain un- 

 developed for a time, and then, instead of forming a 

 normal branch, they grow erratically, and form a swelling 

 or woody tumour of irregular shape, which may attain 



