…kidneys do in fact involve a metabolic process in the creation of urine. The following is from Encyclopedia Britannica, under Urinary System, vol. 22, p. 797b:
"Whereas the energy for the process of filtration is supplied by the heart, the energy for tubular reabsorption must be made available locally by the metabolism of the tubule cells; this reabsorption energy is transmitted through what are probably fairly complicated enzyme systems, each system being more or less specific for each reabsorption process."
I may find other, or more, information that will allow me to confidently link the kidneys with the first appearance of metabolism...
The other issue concerning the kidneys is there fairly high utilization of osmosis. Although I continue to contend that that the lungs are the primary organ of osmosis, it might be safe to say that the kidneys are the body's second organ of osmosis. There are two issues (thus far) that this issue raises: one, the question of whether it is significant that both the kidneys and the lungs are symmetrical organs, and, two, whether or not the presence of osmosis in the kidneys has any significant bearing on the current operational mode of the human imagination.
The symmetry issue should, perhaps, be better explored when dealing directly with the lungs, meaning the relation between symmetry and osmosis. Otherwise, the symmetry of the kidneys is still an issue in terms of its contrast with the asymmetry of the adjacent organs of digestion, but, then again, I can make a point of how the [kidney] symmetry came about through the workings of osmosis, i.e., equilibrium.
In "Our Part," I am about to discuss metabolism as an operational mode of the imagination. I am beginning to realize that this is a very new concept, at least the naming it as 'metabolic' is. The notion of duality is already present in the philosophy of Descartes and after, but the notion that part of our imagination is simultaneously destructive and creative, and calling this process metabolic, is an entirely new use of the word. Assimilation already has a meaning beyond the physiological function, but metabolism does not.
From Donald J. Wilcox, The Measure of Times Past, pp. 46-7:
"When he studied physiology under Burke . . . Freud offered a major alternative to Descartes' separation of subject and object."
In light of what I read today in The Allusion of Technique, chapter "The Two Worlds," my ideas concerning the duality, both metaphorically and physiologically, that is introduced by the kidneys, can be nicely explained, historically, by Descartes at the beginning and ending with the Eros and Thanatos opposition of Freud. Ending with Freud will bring "Our Past" right up to the "our present," and that may well be the major message behind the rest of the "Our Past" chapter.
This may be as good a place as any to begin the case for the new duality, and it is interesting that it is exactly the unity of the Copernican world view that has been undone. I had already seen, in the body, how it is the kidneys that end the singularity of the navel, and now the singularity/duality connection in philosophy is also amazingly similar, and just as straight forward.