Burr Cartwright Brundage notes that the Aztecs performed a baptism of fire in the family hearth on infants four days after their birth.
Burr Cartwright Brundage, The Fifth Sun: Aztec Gods, Aztec World (Austin, Texas: University of Texas Press, 1979), 182, 183
The Nahualli
The concept of the nahualli is peripheral to the Aztec’s concept of his fate. In addition to his soul a man cold possess, as part of the power of his personality, a special affinity for an animal or some other aspect of nature. When considered in this fashion a man was a nahualli, a transcorporate being. The etymology of the Nahuatl word is uncertain, but it meant two rather different things to the Aztecs.
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There was a related concept which was democratic in the sense that it was not restricted to the rare individual but applied to every individual in the society. This could take concrete form in the baptism of the newborn child in the family fire four days after birth; in this ceremony, the child might be dedicated to an animal appropriate to his birthdate. Supposedly this closed a magic circle whereby that child when adult would suffer all the dangers and vicissitudes suffered by his individual animal or by his particular species of animals (our sources are often unclear as to that is implied). The animal thus became the personification of that man’s fate and in some readings of the concept the animal’s death caused—indeed was—the simultaneous death of the person. An invisible and indestructible bound thus might unite a man with his animal partner—the two could exist simultaneously or the nahualli could become his animal counterpart while temporarily giving up his own being.