And as to why it is called Purushamedha: The stronghold (pur) doubtless is these worlds, and the Purusha (spirit) is he that blows here (the wind), he bides (sî) in this stronghold (pur): hence he is the Purusha. And whatever food there is in these worlds that is its 'medha,' its food; and inasmuch as this is its 'medha,' its food, therefore (it is called) Purushamedha. And inasmuch as at this (sacrifice) he seizes men (purusha) meet for sacrifice (medhya), therefore also it is called Purushamedha. He seizes them on the central day, for the central day is the air, and the air is the abode of all beings; and, indeed, these victims are also food, and the central day is the belly: he thus puts food in the belly. He seizes them by decades for the obtainment of all food, for the Virâg consists of ten syllables, and the Virâg is all food. Eleven decades 2 he seizes;--the Trishtubh consists of eleven syllables, and the Trishtubh is the thunderbolt, and vigour: with the thunderbolt, with vigour, the Sacrificer thus repels evil from within him.
Forty-eight he seizes at the central stake;--the Gagatî consists of forty-eight syllables, and cattle are of Gâgata (movable) nature: by means of the Gagatî he (the priest) secures cattle for him. Eleven at each of the others;--the Trishtubh consists of eleven syllables, and the Trishtubh is the thunderbolt, and vigour: with the thunderbolt, with vigour, the Sacrificer thus repels evil from about him.
Last of all he seizes eight;--the Gâyatrî consists of eight syllables, and the Gâyatrî is the Brahman (n.): he thus makes the Brahman to be the ultimate thing of this universe, whence they say that the Brahman is the ultimate thing of this universe. These (eight) are sacred to Pragâpati, Pragâpati assuredly is the Brahman, for Pragâpati is of the nature of the Brahman: therefore they are sacred to Pragâpati. When about to bring up the victims, he offers those three oblations to Savitri, with (Vâg. S. XXX, 1-3), 'God Savitri, (speed the sacrifice, speed the lord of sacrifice unto his share)!'--'May we obtain that glorious light of the God Savitri, (who shall inspire our prayers)!'--'All troubles remove thou from us, O God Savitri: bestow unto us what is auspicious!' He thus pleases Savitri, and thus pleased with him, he (Savitri) impels (speeds) those (sacrificial) men, and he seizes them impelled by that (Savitri). For the priesthood he seizes a Brâhmana, for the Brâhmana is the priesthood: he thus joins priesthood to priesthood;--for the nobility he seizes a Râganya, for the Râganya is the nobility: he thus joins nobility to nobility;--for the Maruts (he seizes) a Vaisya, for the Maruts are the clans (peasants): he thus joins peasantry to peasantry; for (religious) toil (he seizes) a Sûdra, for the Sûdra is toil: he thus joins toil to toil; according to their particular form he thus supplies these divinities with victims, and, thus supplied, they supply him with all his objects of desire. He makes offering with ghee, for ghee is fiery mettle: by means of fiery mettle he thus endows him (the Sacrificer) with fiery mettle. He makes offering with ghee, for that--to wit, ghee--is the dear resource of the gods: he thus supplies them with their dear resource, and, thus supplied, they supply him with all his objects of desire. By means of the Purusha Nârâyana (litany), the Brahman priest (seated) to the right (south) of them, praises the men bound (to the stakes) with this sixteen-versed (hymn, Rig-v. X, 90, Vâg. S. XXXI, 1-16), 'The thousand-headed Purusha, thousand-eyed, thousand-footed. . .;'--thus (he does) for the obtainment and the securing of everything, for everything here consists of sixteen parts, and the Purushamedha is everything: in thus saying, 'So and so thou art, so and so thou art,' he praises and thereby indeed magnifies him (Purusha); but he also thereby speaks of him, such as he is.
Now, the victims had had the fire carried round them, but they were not yet slaughtered. Then a voice said to him, 'Purusha, do not consummate (these human victims 1): if thou wert to consummate them, man (purusha) would eat man.' Accordingly, as soon as fire had been carried round them, he set them free, and offered oblations to the same divinities, and thereby gratified those divinities, and, thus gratified, they, gratified him with all objects of desire.
By the way, the part at the end about the voice contains a pun. Purusha, in addition to denoting Vishnu's Vyuha form Aniruddha, the deity of the Purusha Sukta as I discuss here, is also the Sanskrit word for man. So it's saying "If Purusha eats man, then man will eat man."