REGULATORY PROCESSES IN ORGANISMS 183 
in the organism or part which constitutes a unity distinct to a 
certain extent from others. 
When we investigate the processes in the organism, we find that 
they are very intimately connected with one another: a change in 
one conditions changes in others. Moreover, and this is an impor- 
tant point, the physiological specification of different parts is not 
in most cases absolute. In the highest, most complex forms abso- 
lute specification is doubtless approximated more or less closely 
in certain organs, but in general we find that the processes in differ- 
ent parts of the organism are not fixed in character. The character- 
istic series of reactions in a part does not represent the only pos- 
sible series, but rather the particular series determined by a par- 
ticular complex of conditions. A certain process may occur at one 
time in a certain part, at another time in others. In short there 
is more or less possibility of substitution among the different 
parts. 
Let us suppose, for example, that a certain correlative factor x 
originates in a certain part. Under certain conditions this factor 
may influence various other parts,a b c—n,of whichone, a,let us 
say, reacts with greater speed or intensity than others. The 
reaction of this part may itself produce new correlative factors and 
so alter conditions in the others that their reactions are changed. 
But if we suppose that the receptivity of the part a to the cor- 
relative factor x 1s decreased, or that the part a is itself removed or 
rendered incapable of reaction, then the reactions of a b—n or 
of some of them are not altered or prevented by the effect of the 
reaction of a, and these parts may take the place of a in the sys- 
tem, though perhaps at first reacting more slowly or less intensely 
than a, until their constitution has become altered by repeated 
or continued reactions. 
Through such a series of reactions the individuality of the organ- 
ism is maintained, or restored, even though it may have lost a part. 
We see exactly such reactions in various organisms, and we can 
devise physico-chemical systems which show similar correlation 
between parts and a similar method of maintenance or restora- 
tion of something approaching the preéxisting condition. In the 
system which we devise such processes are processes of equili- 
