Śatapatha Brāhmaṇa ("of a hundred paths") 1.5.4.1

1.5.4.1

sa vai samidho yajati | prāṇā vai samidhaḥ prāṇānevaitatsaminddhe prāṇairhyayam puruṣaḥ samiddhastasmādabhimṛṣeti brūyādyadyupatāpī syātsa yadyuṣṇaḥ syādaiva tāvacaṃseta samiddho hi sa tāvadbhavati yadyu śītaḥ syānnāśaṃseta tatprāṇānevāsminnetaddadhāti tasmātsamidho yajati

He (accordingly) pronounces the offering-prayer to the Samidhs (kindling-sticks). The Samidhs (kindlers), doubtless, are the breaths (vital airs), and he thereby kindles the breaths; for this man (the sacrificer) is kindled (animated) by his breaths: hence if he (the sacrificer) be burning (with fever, &c.), he (the Adhvaryu) will say, 'Stroke (thyself)!' If he be hot, then one may feel confident, for then he is kindled; and if he be cold, then one need hope no longer. Thus he thereby puts the breaths into him: this is the reason why he pronounces the prayer to the Samidhs.