The Srutis speak of the cow as the only food, in the following sense. The cow gives milk. The milk gives butter. The butter is used in Homa. The Homa is the cause of the clouds. The clouds give rain. The rain makes the seed to sprout forth and produce food. Nilakantha endeavours to explain this in a spiritual sense. There is however, no need of such explanation here.
 What Yudhishthira means
to say is that there is no special
time for a Sraddha. It is to be performed whenever a good and
able priest may be secured.
Vaisampayana continued,—“Then agreeable to the words of the Yaksha the Pandavas rose up; and in a moment their hunger and thirst left them. Thereupon Yudhishthira said, ’I ask thee that art incapable of being vanquished and that standest on one leg in the tank, what god art thou, for I cannot take thee for a Yaksha! Art thou the foremost of the Vasus, or of the Rudras, or of the chief of the Maruts? Or art thou the lord himself of the celestials, wielder of the thunder-bolt! Each of these my brothers is capable of fighting as hundred thousand warriors, and I see not the warrior that can slay them all! I see also that their senses have refreshed, as if they have sweetly awaked from slumber. Art thou a friend of ours, or even our father himself?’ At this the Yaksha replied,—’O child, I am even thy father, the Lord of justice, possessed of great prowess! Know, bull of the Bharata race, that I came hither desirous of beholding thee! Fame, truth, self-restraint, purity, candour, modesty, steadiness, charity, austerities and Brahmacharya, these are my body! And abstention from injury, impartiality, peace, penances, sanctity, and freedom from malice are the doors (through which I am accessible). Thou art always dear to me! By good luck thou art devoted to the five; and by good luck also thou hast conquered the six. Of the six, two appear in the first part of life; two in the middle part thereof; and the remaining two at the end, in order to make men repair to the next world. I am, good betide thee, the lord of justice! I came hither to test thy merit. I am well-pleased to witness thy harmlessness; and, O sinless one, I will confer boons on thee. Do thou, O foremost of kings, ask of me boons. I shall surely confer them, O sinless one! Those that revere me, never come by distress!’ Yudhishthira said,—’A deer was carrying away the Brahmana’s fire-sticks. Therefore, the first boon that I shall ask, is, may that Brahmana’s adorations to Agni be not interrupted!’ The Yaksha said,—’O Kunti’s son endued with splendour, it was I who for examining thee, was carrying away, in the guise of a deer, that Brahmana’s fire-sticks!’”
 That is, tranquillity
of mind, self-restraint, abstention
from sensual pleasures, resignation, and Yoga meditation.