From the Supplement, compiled after Aquinas’s death from his Commentary on the Sentences and transcribed here from the 1917 to 1922 printings. About the Supplement.
Text: Summa Theologiae, Supplement to the Third Part (Supplementum Tertiae Partis), transcribed from Internet Archive scans, translated by the Fathers of the English Dominican Province. The Supplement, compiled after Aquinas’s death from his earlier Commentary on the Sentences, in the same English Dominican translation as the Gutenberg Parts. Transcribed by Bibliotheca Catholica from the OCR of four Internet Archive scans of the pre-1931 printings (Questions 1 to 33 from the 1917 Washbourne and Benziger volume, 34 to 68 from the 1922 volume, 69 to 86 from the 1921 volume, and 87 to 99 from the 1922 Benziger volume), with OCR errors corrected and doubtful passages marked, not rewritten. 99 questions and 446 articles. The two appendices printed after Question 99 are not included. Sources, SHA-256 of each OCR file, and the method are in the source record. Rights: Public domain (US)
The Supplement is not a Project Gutenberg text. It is Bibliotheca Catholica’s transcription of public-domain scans at the Internet Archive; obvious OCR errors were corrected, and passages marked “OCR uncertain” could not be confidently corrected, so check them against the linked scan page.
Objection 1: It seems that even a layman can confer this sacrament. For this sacrament derives its efficacy from prayer, as James declares (v. 15). But a layman's prayer is sometimes as acceptable to God as a priest's. Therefore he can confer this sacrament.
Obj. 2: Further, We read of certain fathers in Egypt that they sent the oil to the sick, and that these were healed. It is also related of the Blessed Genevieve that she anointed the sick with oil. Therefore this sacrament can be conferred even by lay people.
On the contrary, Remission of sins is given in this sacrament. But laymen have not the power to forgive sins. Therefore etc
I answer that, According to Dionysius (Eccl. Hier. v.) there are some who exercise hierarchical actions, and some who are recipients only. Hence laymen are officially incompetent to dispense any sacrament: and that they can baptize in cases of necessity, is due to the Divine dispensation, in order that no one may be deprived of spiritual regeneration.
Reply Obj. 1: This prayer is not said by the priest in his own person, for since sometimes he is in sin, he would not in that case be heard. But it is said in the person of the whole Church, in whose person he can pray as a public official, whereas a layman cannot, for he is a private individual.
Reply Obj. 2: These unctions were not sacramental. It was due to the devotion of the recipients of the unction, and to the merits of those who anointed them that they procured the effects of bodily health, through the grace of healing (i Cor. xii. 9) but not through sacramental grace.
_______________________
Also online, linked only: the same translation at New Advent and the Latin text at Corpus Thomisticum. Neither is copied here.