WHITE AND YELLOW YOLK OF OVA 471 
histologists; but which has apparently not gained universal accep- 
tance: A spherule of yellow yolk may arise from a spherule of white 
yolk; in the normal destruction and utilisation of the yellow spherule, 
a white spherule may be again produced. 
i Lhe part played by the reversible action of enzymes 
Kastle and Loevenhart (00) proved the reversibility of the 
action of lipase—the enzyme concerned in the analysis and syn- 
thesis of fat; and we have seen that fat is the chief constituent of 
yolk. Wohlgemuth (’05) demonstrated the presence of lipase in 
the yolk of the fowl’s egg. It was shown by Henriques and 
Hansen (’03) that the fatty acids of the food, z.e., of foreign fat, 
are laid down as such in the hen’s egg. Since we know that this 
fat did not originate within the egg; and, since we are assured 
that fat as such does not pass through living cells, but that it is 
previously split into alcohol and constituent fatty acids, we must 
believe that the foreign fat found by Henriques and Hansen was 
synthesized within the egg cell; or, that it was synthesized in the 
neighboring follicular cells and thrown from their inner margins 
into the egg. This last alternative is not true as will be pointed 
out later. 
Thus we come by means of the above series of facts directly to 
the proof of the existence within the fowl’s egg of the synthesis— 
one side of the enzyme action—of the most voluminous constitu- 
ent of the yolk. 
Has the existence of the splitting action of lipase in the egg also 
been demonstrated? I believe it has practically been so dem- 
strated by Liebermann’s (’88) determination that only the merest 
traces of free fatty acids are present in the fresh egg, whereas large 
amounts are present at seven and fourteen days of incubation. 
The existence of a splitting activity of lipase in the hen’s egg is 
moreover a matter that probably no one will question. From 
these facts then I think it must be said that the reversible action 
of lipase within the hen’s egg has been indirectly demonstrated. 
In fact, one familiar with the picture presented by the deposit 
and absorption of the yolk of eggs, can but wonder that this pic- 
ture has not been before specifically pointed out as an example— 
JOURNAL OF MORPHOLOGY, VOL. 22, No. 2 
