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 
17 
