THE CAUSATION OF DISEASE. 349 



unused embryonic tissue, although it does not entirely 

 exclude a specific E from, a share in causation, obviously 

 refers a large part of causation to peculiarity of S in the 

 shape of unused embryonic tissue. This theory is at once 

 improbable and useless. We do not find, except perhaps in 

 a few cases of sarcomata, that malignant growths have a 

 predilection for parts where we should expect such embryonic 

 remains to abound. There is no part of the body which 

 may not be affected with some one or other form of malig- 

 nant disease. Local irritation, rather than embryonic remains, 

 determines the exact site. This is very noticeable in epithe- 

 lioma. Why should embryonic remains be more particularly 

 present in such part of the tongue as lies under a sharp 

 tooth, or in those parts of the alimentary canal most subject 

 to irritation ? Indeed, if the embryonic view be correct, 

 embryonic remains must be scattered throughout the whole 

 body, and this surely robs the theory of all its force. And 

 it is not only an improbable, it is a useless, theory — it explains 

 nothing. If there were distinct evidence that the entire 

 tumour in all cases originated from the first few cells consti- 

 tuting it, the fact would be in favour of the embryonic theory ; 

 but. inasmuch as it can be proved that in many cases of 

 malignant change the tumour is formed by a transformation of 

 previously existing mature tissue, the theory is useless, for we 

 can do without it. It may perhaps help us to explain inno- 

 cent growths, but it in no way helps us to explain the leading 

 characteristic of malignant growths, viz., their infectiousness. 



I said that malignant change was a retrogressive one. In 

 all cases of new formation occurring as the pure outcome of 

 heredity, the change is evolutionary, from the homogeneous to 

 the heterogeneous, from the less complex to the more complex. 

 Malignant change, on the other hand, is essentially dis- 

 solutionary. We are thus led to discuss the nature of 

 sarcomatous and carcinomatous tissue. All agree that the 

 tissue of sarcoma is of a very elementary kind. The same 

 kind of tissue is abundantly met with in the embryo and in 

 the simpler forms of life. The sarcomatous change is, there- 

 fore, a reversion ; it is the manifestation of one of the many 



