The Jass

From Charles J. Billson's article on  a Swiss tradition"The 'Jass' at Thun" (1908) (Billson also employs one of my favorite words, bugbear):

At Thun, in Switzerland, the annual Shooting Feast takes place in October, when three days are devoted to making holiday.  One of the tallest and strongest boys in the town is previously selected by the schoolmasters for the honour of appearing during the feast in the costume of a "Jass" or Jester, shown in the accompanying photograph.  His mission is to walk about the town and belabour with his baton all the youngsters whom he can catch.  During the rest of the year the "Jass" is held up as a bugbear wherewith mothers and nurses threaten their children, telling them that, if they are not good, the "Jass" will catch them, and give them a beating.   Another name given to the "Jass" is "Fulla Hund," i.e. Fauler Hund, "Lazy Dog."