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PHYSIOLOGY: C M. CHILD 
are characteristic of levels of the body anterior to the level from which 
it was taken, unless a head first begins to develop. On the other hand, 
any piece is capable of producing parts characteristic of more posterior 
levels than its own, even in the complete absence of a head. These 
facts mean essentially that each level of the body is dominated by 
more anterior levels, but in their absence itself dominates more posterior 
levels and that the head region dominates all levels within a certain 
variable limit of distance. 
It has also been shown by many authors that small isolated pieces 
of the body of various simple animals may undergo reconstitution into 
apical structures or heads without the presence or formation of any 
other parts of the body, but in no case has a posterior or basal structure 
arisen, except in connection with and as an outgrowth from more apical 
or anterior parts. In other words, the apical region or head of the 
organism is capable of developing independently and in the complete 
absence of other parts, while the formation of other regions of the body 
is dependent upon the presence of more apical or more anterior parts. 
This relation between apical or anterior regions and other parts is of 
fundamental importance for our conception of the organism, but, so far 
as I am aware, attention has not been called to its significance by those 
who have observed and recorded many of the facts. 
In some of the lower animals it is even possible to eliminate experi- 
mentally the original gradient and then to produce a new gradient in 
the cell mass in a different direction. In such cases the original axis of 
the organism disappears and a new development takes place along an 
axis coincident with the newly established gradient, the region of highest 
rate in the gradient becoming the apical part of the new individual. 
The dominance of the apical region, the growing tip, over other parts 
of the axis in the plants has long been known to botanists and it has 
been demonstrated repeatedly that this dominance can be decreased or 
eliminated and so the relations in space or time of other parts altered, 
by decreasing or inhibiting metabolic activity in the dominant region. 
Essentially the same relations imdoubtedly exist along the axis in both 
plants and animals, but this very important fact has apparently not 
been recognized. 
These and various other experimental data which cannot be men- 
tioned here point us very definitely to the conclusion that the organic 
axis in its simplest form in both plants and animals is a gradient in 
rate of metabolism or of certain fundamental metabolic reactions, per- 
haps primarily the oxidations, and that such a gradient is at the same 
