470 OSCAR RIDDLE 
I purpose to preface this inquiry with a statement of my two 
main conclusions, or theses. (1.) The formation and the de-forma- 
tion of yolk are one and the same subject. The processes of bualding 
are also the processes of tearing-down; only an equilibrium changes. 
These two sister-subjects have, however, long paraded as inde- 
pendents. The formation of yolk has been considered a subject 
the investigation of which was connected with a wide variety of 
study such as the migration of fully-formed yolk granules from 
follicular cells into the ovum; the origin of yolk granules from 
migrated particles of the chromatin, or the nucleolus; or again 
their formation by the yolk nucleus, or by mitochondria, etc. On 
the other hand, when the other phase of yolk metabolism—its 
de-formation—was concerned, observers have been pretty gener- 
ally satisfied to speak only of ‘a digestion and ingestion of yolk.’ 
(2.) Given a region into which the elements of yolk—with their 
vast amount of potential energy—can go and can exist without under- 
going oxidation, and yolk (or some of its elements) will there be in- 
creased or decreased 1n amount subject to an equilibrium which is 
a function of two factors; (a) the reversible action of enzymes and, 
(b) the partition coefficient of the elements of yolk. We do not state 
that all desirable proof of this thesis is at hand, but we do insist 
that a very considerable body of evidence supports it. Having 
been led to the formulation of this view, and to the acceptance of 
it to the fullest extent ourselves, we shall here outline the evidence 
which we believe will likewise commend it to others. 
It is not necessary to discuss separately what we have called 
theses one and two. Both rest upon the question of the presence, 
the effectiveness, and the modus operandi of the two factors which 
we have proposed as the immediate agentsof yolk transformations; 
whether such transformations be of growth or of ‘digestion,’ 
whether they be progressive or regressive in character. The dis- 
cussion therefore hangs upon these factors and we shall consider 
them separately. 
Before proceeding in this direction, however, it is well to be 
reminded that these theses are the physiological and explanatory 
counterpart of an histological dictum which in certain of its as- 
pects has been for many years ably maintained by several noted 
