Daniel G. Brinton 
Nagualism: Aztecs Folklore and Magic 

The words, a nagual, nagualism, a nagualist, have been current in English prose for more than seventy years; they are found during that time in a variety of books published in England and the United States, yet are not to be discovered in any dictionary of the English language; nor has Nagualism a place in any of the numerous encyclopaedias or ‘Conversation Lexicons, ‘ in English, French, German or Spanish. This is not owing to its lack of importance, since for two hundred years past, as I shall show, it has been recognized as a cult, no less powerful than mysterious, which united many and diverse tribes of Mexico and Central America into organized opposition against the government and the religion which had been introduced from Europe; whose members had acquired and were bound together by strange faculties and an occult learning, which placed them on a par with the famed thaumaturgists and theodidacts of the Old World; and which preserved even into our own days the thoughts and forms of a long suppressed ritual.