most private of organs

[NewHope]

Is "private" an adjective?

Context:

While innate processing, instinctive behavior, internally orchestrated motivation and drive, and innately guided learning are all essential and important elements of an animal’s cognitive repertoire, they are not likely to be part of that more esoteric realm of mental activity that we associate with thinking, judgment, and decision-making. But what is thought, and how are we to recognize its operation in other creatures within that most private of organs, the brain? What behavioral criteria can permit us to distinguish between the true thought that we are wont to believe goes into our aesthetic, moral, and practical decision-making on one hand, and the intricate programming that can create the illusion of thought in at least certain other animals? Or could it be, as advocates of artificial intelligence suspect, that all thought, including ours, is just the consequence of clever programming?

Yup.

This is my private journal.
This room is private.
Is this conversation private?

I think that the only time it can be a noun is in reference to the lowest military rank - a private - and, perhaps, in reference to those other "most private of organs" - your privates! ;)

Hope this helps!