PHYSIOLOGY: C M. CHILD 
167 
or less distance from this region arises, because the changes in the prim- 
ary region spread or are transmitted, but with a decrement in intensity 
or energy, so that at a greater or less distance from the point of origin 
they become inappreciable. It is evident that in general transmission 
of this sort must occur from a region of higher to one of lower rate of 
reaction, and S. Tashiro has found that this rule holds for the special- 
ized form of transmission which is found in nerves. Thus the region of 
higher rate, once estabHshed, becomes an important factor in determin- 
ing the rate of other regions, and since the rate thus determined is higher 
in regions nearer to it and lower in those farther away, a gradient results. 
Since the region of high rate of reaction determines the existence of the 
gradient, it becomes the chief factor in determining the rate of reaction 
in other regions within the range of its influence and therefore in de- 
termining the sequence of events in time and space in these parts. Con- 
sequently it appears to dominate or control other regions and they to 
be subordinate to it. It is evident that according to this conception the 
degree of dominance and subordination and the range of influence of the 
dominant part must depend primarily upon two factors. The first of 
these is the difference between the metabolic rate of the dominant part 
and the intrinsic rate of other parts before they were influenced by it. 
The higher the rate in the dominant region above the original intrinsic 
rate of the cell or cell mass the greater its effect in increasing the rate in 
other parts and the greater the distance to which its influence extends. 
The second factor is the efficiency of transmission. Where the trans- 
mitted changes influence other parts but slightly and soon die out, domi- 
nance is sHght and limited to short distances from the dominant part, 
but where the decrement in the course of transmission is sHght, as in 
the nerves of higher animals, the influence on the dominant part may 
make itself felt at very great distances. 
I have been able to demonstrate experimentally in various ways this 
relation of dominance and subordination and to show that the axial 
gradient is an essential factor in determining the orderly formation of 
parts and their relations in space and time to each other. (For some 
of the experiments on Planaria see references 1, 3, 7. Various other 
data on coelenterates and flatworms are as yet unpublished.) For ex- 
ample, in the reconstitution of pieces of Planaria into new whole ani- 
mals, the higher the metabolic rate in the developing head region, the 
farther away from the head do the pharynx and mouth appear, and 
vice versa, and other parts of the body show similar relations. Any 
piece of the planarian body is incapable of giving rise to any parts which 
