476 OSCAR RIDDLE 
constituents. For such to be set free now, however, is to leave 
the egg entirely; for now the distribution coefficient of each of 
such substances brings a portion of it into the blood or lymph; 
and here it is not allowed to accumulate—to saturate this solution 
and then cease to act,—but is taken up by other organs; while the 
blood thus freed from traces of it continues to pick up more of 
such particles as it passes the ovum. Because of this principle 
then an ovum may not be able to hold all the yolk that it has once 
acquired. Apparently we can explain the broad zones of white 
yolk in the turtles in this way, and the known facts seem to re- 
quire the mechanisms we have described. 
Of course we do not mean to infer that no other factor than the 
two we are describing have to do with certain aspects of yolk 
metabolism. For example, these two may have little causative 
influence in deciding that very important matter as to when the 
rapid growth of the hen’s yolk is to begin. Here le mysteries 
perhaps of the follicular cells, or something else, perhaps more dis- 
tant from the point of actual yolk formation. We are dealing 
only with the immediate mechanism of yolk formation and de- 
formation. 
The possible réle of lecithin in increasing the solubility of fatty 
acids and soap in the follicular cells and in the yolk is an attractive 
subject. Moore and Parker (’01) have shown how enormously 
the solubilities of these substances are increased by the addition 
of small amounts of lecithin and bile salts. I have ascertained 
the presence of lecithin in the follicular membranes, but as yet 
have not enough analyses for comparison to draw conclusions. I 
have determined also, as is indicated in Table II, that the leci- 
thin content of the white yolk—i. e., the layer just beneath follic- 
ular membrane, and usually between it and the yellow yolk— 
is smaller in amount than that of the yellow yolk. 
As a concluding word on the réle of the partition coefficient we 
record our belief that it alone accounts for the presence of the 
yolk coloring matters—vitello-lutein and vitello-rubin—in the 
yellow yolk, and not in the white. These are lipochrome pigments, 
soluble only in fat and fat solvents, and are abundant in the large 
yolk spherules, probably because, as we have shown by compara- 
