MorGan: Hyporuesis OF FORMATIVE STUFFS 213 
In my book, ‘‘ Regeneration,”’ I offered, as a pure conjecture, 
the suggestion that this physical factor expresses itself in the form 
of different tensions in the living tissues. Goebel asks whether 
such a conception puts the question in any clearer light than before. 
I am inclined to think that the idea is not entirely worthless, and 
it should not be forgotten that I pointed out, as emphatically as 
possible, that the view is only conjectural and must be tested by 
further work. It was offered as a possible working hypothesis, 
and it is unfair to treat the suggestion in any other light. If the 
view appears too vague it can be given a more practical form by 
assuming that the differences in tensions are simply the outcome 
or expression of osmotic changes, which are themselves in turn the 
result of the presence of certain chemical substances present, or 
being produced in the organism. * 
BryN MAWR COLLEGE, 
* Since the above was written Matthews has suggested that my tension-hypothesis 
may be an expression of the electrical conditions in the piece; in short, that ‘* po- 
larity’ is an electrical phenomenon ; possibly, I may add, due to the movement of ions. 
