Heather,

I, too, find the sponge analogy very helpful.  It is described in a chapter
by Michael Woolridge, "Baby-Controlled Breastfeeding: Biocultural
Implications" in the book, Breastfeeding: Biocultural Perspectives, (edited
by Patricia Stuart-Macadam and our own Katherine A. Dettwyler, published by
Aldine de Gruyter, 1995).  Look on p. 238 under footnote number 6.  I'll
quote just a little bit:

"Hytten (1954) proposed and tested a physical model of milk storage and
delivery.  He immersed a natural sponge in whole milk and left it for some
period, then gradually compressed milk from the sponge; the first milk
draining off was low in fat, similar to foremilk, and with progressive milk
removal the fat concentration rose, finally approximating to hindmilk.  The
explanation he proposed was that fat droplets, being adherent, became
adsorbed onto the internal luminal walls of the sponge, and that sustained
milk removal was necessary to dislodge the adherent fat.  His physical
model of storage and delivery duplicated the changes in fat concentration
during milk removal sufficiently closely that it has not been necessary to
invoke further models..."

There is more discussion on this point by Woolridge, and I recommend
reading this footnote, chapter (and the whole book, as it is excellent!) in
its entirety.

And now I must not look at Lactnet any more for at least the next 24 hours!

Anne Altshuler, RN, MS, IBCLC and LLL leader in Madison, WI
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