REGULATORY PROCESSES IN ORGANISMS 189 
The question at once arises as to whether all processes of equili- 
bration are to be regarded as regulations, or only certain of them. 
By zodlogists the term ‘regulation’ has been applied mostly to 
processes occurring under experimental conditions outside the 
usual range of conditions in nature and the regulations of formand 
structure have been the chief, though not the only objects of inves- 
tigation. Jennings (’06) has used the term with reference to 
phenomena of behavior which are characteristic features of life and 
not of abnormal or pathological conditions. Among the physiolo- 
gists also we find the term often used as referring to various 
changes in metabolism and reactions of different kinds in response 
to conditions to which every individual is subjected repeatedly. 
If we define regulation as a return or approach to a condition of 
dynamic equilibrium in a living organism after a previously exist- 
ing condition has been disturbed by some external factor (Child,’06), 
we shall include all the above phenomena as well as many others. 
According to this definition, the simplest reflex as well as the 
restoration of a missing part is a regulation, the simplest correla- 
tive compensation in metabolism, as well as the development of 
a whole from an isolated blastomere of an egg. 
Moreover, when a complex part of an organism undergoes an 
equilibrating change in reaction in response to altered correlation 
with another part or other parts, a regulation occurs as truly as 
when the whole organism responds to some change in conditions 
outside of it. In short, regulations are equilibrating reactions to 
changes external to the reacting system, whether this system be a 
part or a whole of an organism. 
And finally, regulation is not limited to the return or approach 
to the preéxisting condition, but may be an approach to a condi- 
tion very different from that, 7.e., the organism or the part may 
become something more or less widely different from what. it 
was originally. In every case of regeneration of lost parts some of 
the cells become something different from what they were before 
the part was removed, and their change is a reaction to altered 
conditions and specifically to altered correlation. 
But that the regulatory process is always and necessarily of 
advantage to the organism does not follow from the definition. 
