What bioethics did was also reverse this dictum to end of life issues -- and this was taught in a major seminar at a Georgetown bioethics conference early on (about 1990). Those of us in the seminar on "euthanasia" were taught that -- just as there is a series of souls at the beginning of life -- at the end of life the reverse happens (supposedly adapted from St. Thomas): in the dying patient, first the rational soul leaves the body, then the sensitive soul leaves the body, and finally the only thing left there in the patient is the vegetative soul -- and thus there is no "person" really present! Of course, that would also mean that with euthanasia, physician assisted suicide (PAS), and organ transplantation, the use of such "vegetables" in human research, etc., would be "ethical". This concept of the "vegetative state" was immediately picked up by one of the first new bioethics international centers in France -- INSERM. They were the ones who really popularized the phrase.
As an Aristotelean Thomist myself, I wrote an article on this last year, with extensive direct quotations from both Aristotle and St. Thomas, using the wonderful encyclical of Pope Leo XVIII as a backdrop: “’Revival’ of St. Thomas’ Philosophy – Yes, But Not His Erroneous ‘Delayed Personhood’ Argument; Concerns for Beginning and End of Life Issues” (April 4, 2011), at: http://www.lifeissues.net/writers/irv/irv_185revival.st.thomas1.html.
Dianne Irving, Ph.D.