REGULATORY PROCESSES IN ORGANISMS Wig 
be removed. Fortunately the embryologists themselves have now 
a method of removing these granules from their usual position, 
z.e., the method of centrifuging the egg, and the results of recent 
experiments along this line indicate, as was to be expected, that 
the granules are quite unessential to regional localization and dif- 
ferentiation of the embryonic structures. 
It is evident from the above suggestions that our fundamental 
conceptions of the relation between structure and function in 
organisms must be intimately connected with our ideas concerning 
the nature of colloid substances and their significance as a sub- 
stratum or medium for chemical reactions. Within recent years 
it has beea pointed out repeatedly that these substances afford 
various means for the partial or total isolation of different chemi- 
cal reactions in organisms and that their mere presence may bring 
about such isolation, e.g., by the formation of semipermeable mem- 
branes. Here then we have a physico-chemical basis for localiza- 
tion and differentiation. Moreover, the changes in the physical 
aggregate condition of colloids, together with the possibility of 
the simultaneous existence of different phases of high and low 
water-content, must play a part in determining the degree and 
place of dissociation of various substances, and therefore in de- 
termining the speed of reactions in different regions, as well as 
the occurrence or non-occurence of certain reactions at partic- 
ular points. It is then, to say the least, highly probable that 
the possibilities of localization, physiological specification and - 
the accompanying possibilities of physiological correlation of 
parts and of regulation are very closely connected with the fact 
that the formation of colloids is a component of the reaction 
complex known as metabolism. Moreover, as I have attempted 
to show in another paper (Child, ’11b), the accumulation of rela- 
tively inactive substances, particularly colloids, in the cell is 
undoubtedly a factor in senescence, in that it constitutes an 
obstacle to the metabolic interchange and so brings about a de- 
crease in the rate of metabolism. 
If the conclusion be correct, that the visible structural elements 
of the cell are, at least for the time being, relatively inactive chem- 
ically, thea it follows that these elements do not represent the 
