WHITE AND YELLOW YOLK OF OVA 481 
are the inferences that have too often accompanied it to the effect 
that the structure about which yolk ts found to form, is itself the 
active agent in the yolk formation. From the facts already brought 
forward we see that whatever the out-wandering chromatin par- 
ticle—the invisible td or biophor—may be able to accomplish 
in directing the course of differentiation in the highly complex 
living cytoplasm, the building of a single inert yolk granule by a 
plainly visible amount of chromatin is a task which clearly quite 
surpasses it! At any rate a task which it does not accomplish. 
Yolk formation as it is indicated by the facts presented in this 
paper may be connectedly outlined as follows: Yolk will be 
formed (1) when conditions are such in the egg, follicular cell, 
food-supply, or organism that excess of food may enter the egg; 
but (2) in those regions only where some excess of food fat (and 
protein) can exist without undergoing oxidation; (8) the main- 
tenance of such excess of food is dependent upon the amount of 
food, or upon marked fluctuations in the amount of food outside 
the egg, and (4) upon the distribution coefficient of the elements 
of yolk in the substance inside and immediately outside of the 
egg, and doubtless by other undetermined conditions within the 
egg; (5) the actual and active processes of yolk increase or decrease 
are essentially identified with the partially known synthetic 
and analytic,—7.e., reversible-action of the-enzymes which act 
upon the constituents of yolk; (6) in the first stages of the growth 
of a (white yolk) yolk spherule the proportion of fats and phos- 
phatids in its composition is small; (7) in later and more com- 
plete (yellow yolk) stages the proportion of these constituents 
is large. | 
In my opinion what we now most need to know is how those 
conditions arise which permit yolk-building to begin. We need 
further knowledge on*points (1) and (2) of the above. That is, 
we need to know why an unusual amount of food enters the egg 
at this particular time in its history. At present we do not know 
whether such cause lies inside or outside the egg. Again, what is 
the source of those reduction centers where foods which yield 
energy so easily as do the fats may not undergo oxidation but be 
built unchanged into yolk? It is possible, of course that nucleus, 
