One of the multitude answered him, Master I brought—the Greek is ἤνεγκα—unto thee my son. He brought his son, expecting to find Jesus; but failing in this, he applied to our Lord's disciples to cast out the evil spirit, but they could not.
St. Matthew (Matthew 17:14) says that the man came kneeling to Christ, "and saying, Lord, have mercy on my son: for he is lunatic." The word in the Greek there is σεληνιάζεται. Etymologically, no doubt, "lunatic" conveys the meaning of the word most nearly.
But the graphic description here of St. Mark cot-responds exactly to epilepsy, and to epilepsy acted upon by an unclean spirit, who in this instance deprived the sufferer of his speech. Lunatics were so called from the prevailing impression, not without foundation, that the light and the changes of the moon have an influence upon the body, and so act through the body upon the mind.
This influence seems to be recognized in Psalms 121:6, "The sun shall not smite thee by day, nor the moon by night."