*66 Dr. Clarke’s Account of a Tumour 
If the mere existence of such a tumour is not to be considered 
as a disease, there was no appearance of any morbid tendency 
in any part of it. The whole structure seemed to consist of 
a regularly organized matter throughout, supplied with vessels 
exclusively belonging to itself, and not passing to it from the 
surrounding parts, as is generally the case in diseased masses. 
They who are inclined to consider every new appearance in 
the structure of parts as disease, may be disposed to include 
this under that appellation. 
But disease consists of such an alteration in the structure, 
or functions, of a part, as occasions the natural operations of 
it to be imperfectly performed, or entirely arrested. This tu- 
mour appears to have produced no such effect : all the com- 
mon and known functions of the placenta were performed, 
notwithstanding the existence of this substance : the child 
had been as well nourished, and the benefits arising from the 
application of vital air or oxygen, to its blood, just as well syp- 
plied, as if the tumour had not existed. 
It cannot be said of this, as it might of some tumours, that it 
would in time have shewn marks of a morbid tendency, so as 
to have deranged the common actions of the placenta; because, 
when gestation terminates, the life, and all the uses of the pla- 
centa, are at an end. 
I am disposed, therefore, to consider this fleshy substance, 
as a solitary instance of a formative property in the vessels of 
the placenta; which they have not been hitherto generally 
known to possess.* 
* The placenta sometimes becomes converted into a mass of hydatids, connected to 
each other by small filaments ; but this must be considered as a disease, inasmuch as 
the natural structure is destroyed, and it directly interferes with the offices of the pla- 
