To quote the Ax-man
The acquiring process absorbs only DNA, and that DNA is isolated, encapsulated within your own bloodstream in a super-low temperature--and
thus very stable--naltron molecule sphere."
Book 18
Sounds like DNA is in a little ball that's kepy in the bloodstream, which does seem ludicris as that leaves no direct way for the neural process of "concentrating" to activate it. Less of course it's somehow within the blood stream but tied to the to the nerves of the vessels.
How much/ how many of these there are is also a mystery. If you only have a molecule or single sphere, it doesn't matter how much blood you lose, almost impossible that anyone would find it (so the fear of doctors finding animal DNA in your blood is really nonexistant.)
Course it's 8 am. Everything seems a little ludicris