REGULATORY PROCESSES IN ORGANISMS 179 
2. Physiological correlation and the physiological system or 
indiwidual 
Organisms in general appear in the form of more or less sharply 
defined physiological systems or individuals and in the more com- 
plex organisms we can distinguish systems or individuals of vari- 
ous kind and degree. What is the basis of this unity? 
The experimental investigation of organisms has led those 
who are not yet ready to accept vitalistic hypotheses to the con- 
clusion that two factors are chiefly involved in the formation of a 
living system or individual, viz. constitution and physiological 
correlation. In its grosser aspects the first of these is the morpho- 
logical, the second the physiological factor. Most of us believe, 
however, that the morphological features of organisms are 
essentially visible expressions of dynamic processes past or pres- 
ent and that sooner or later we must interpret constitution in 
dynamic terms. The factor of physiological correlation in the 
organism is essentially the problem of physiology, forin the final 
analysis function is impossible without such correlation. 
Wherever in the universe unity can be recognized, there some 
sort and some degree of correlation must exist, either conceptually 
or as a datum of nature, between the elements which compose the 
unit, and vice versa, wherever correlation between conceptual or 
phenomenal elements is recognized or established, there a unity 
of some sort and some degree exists. On the other hand, the char- 
acter of the unity is determined by the nature or constitution, 
however this may have arisen, of its elements. 
There is at present no adequate ground for believing that organ- 
isms differ from other phenomena in these respects. We cannot 
conceive an organic individual without correlation of some sort 
between the parts which compose it, nor can we conceive it with- 
out elements or parts of a certain more or less characteristic con- 
stitution. 
The development of morphology and its separation from other 
fieldsof biology during the latter half of the nineteenth century has 
led, particularly in the field of zodlogy, to the consideration of the 
problem of constitution apart from that of correlation. But the 
