Bhashya
पुरुषो वा अग्निर्गौतम ; प्रसिद्धः शिरःपाण्यादिमान् पु-रुषः चतुर्थोऽग्निः तस्य व्यात्तं विवृतं मुखं समित् ; विवृ-तेन हि मुखेन दीप्यते पुरुषः वचनस्वाध्यायादौ, यथा स-मिधा अग्निः ।प्राणो धूमः तदुत्थानसामान्यात् ; मुखाद्धिप्राण उत्तिष्ठति ।वाक् शब्दः अर्चिः व्यञ्जकत्वसामान्यात्; अर्चिश्च व्यञ्जकम्, तथा वाक् शब्दः अभिधेयव्यञ्जकः ।चक्षुः अङ्गाराः, उपशमसामान्यात् प्रकाशाश्रयत्वाद्वा ।श्रोत्रं विस्फुलिङ्गाः, विक्षेपसामान्यात् ।तस्मिन् अन्नं जुह्वति ।ननु नैव देवा अन्नमिह जुह्वतो दृश्यन्ते- नैष दोषः, प्राणानां देवत्वोपपत्तेः ; अधिदैवम् इन्द्रादयो देवाः ; ते एव अध्यात्मं प्राणाः ; ते च अन्नस्य पुरुषे प्रक्षेप्तारः ; तस्या आहुतेः रेतः संभवति ; अन्नपरिणामो हि रेतः ॥
In plain words
Man himself is fire, Gautama -- this ordinary person with a head and hands is the fourth fire. His open mouth is its fuel; he blazes through that open mouth whenever he speaks or recites the Veda, exactly as fire blazes through fuel. His breath is the smoke, since breath rises the same way smoke does. His speech, its very sound, is the flame -- a flame reveals things in the dark, and speech reveals meaning the same way. His eye is the coals, since coals dim down just as the eye's brightness settles, or because light itself lives there. His ear is the sparks, scattering the way sparks scatter. Into this fire, food is offered. But someone may object: we never actually see gods offering food here. No fault in that -- because the vital breaths themselves are, quite reasonably, divine. Seen from the side of the deities, Indra and the rest are the gods; seen from the side of the self, those very powers are the breaths. And it is they who carry the food into the person. From that offering, seed comes to be -- because seed, after all, is simply what food becomes.
Close to the Sanskrit
Man, indeed, is fire, O Gautama; the well-known person possessing head, hands, and so on, is the fourth fire. His open mouth is the fuel; for indeed the person blazes through his open mouth in speaking and Vedic recitation and the like, just as fire [blazes] through fuel. The vital breath is the smoke, because of the shared feature of arising therefrom; for indeed breath rises from the mouth. Speech, that is, sound, is the flame, because of the shared feature of being a revealer; flame too is a revealer, and likewise speech-sound is the revealer of what is meant. The eye is the coals, because of the shared feature of subsiding, or because of being the seat of light. The ear is the sparks, because of the shared feature of scattering. Into that they offer food. Now, an objection: the gods are never seen offering food here -- this is not a fault, because of the tenability of the divinity of the vital breaths; at the level of the deities, Indra and the rest are the gods; they themselves, at the level of the self, are the vital breaths; and they are the ones who cast food into the person; from that oblation, semen arises; for indeed semen is the product of food.