What did Ralph use as a model for his behavior as a school master?

The Hoosier Schoolmaster: A Story of Backwoods Life in Indiana is a novel by Edward Eggleston, first published in 1871, that became extremely popular in its time. The writing makes great use of an American dialect called Hoosier, which was, as Eggleston himself explains in the preface he wrote for the library edition of the book, "the folk-speech of the southern part of Ohio, Indiana, and Illinois."
The narrative follows a man named Ralph Hartsook, who takes on the position of schoolmaster at a school in Flat Creek, Indiana. He applied for the job because he believes "that Flat Creek was what he needed" to take him out of his sheltered "bookish life." Despite skepticism regarding whether he will be able to handle the job, he is hired because "They a'n't been no other applications."
The first chapter is titled "A Private Lesson from a Bulldog." When Ralph goes out hunting with Bud and Bill Means, they bring along their bulldog, aptly named Bull. Ralph doesn't exactly enjoy the hunt, but the narration tells us that

When Bull at last seized the raccoon and put an end to it, Ralph could not but admire the decided way in which he did it, calling to mind Bud's comment, "Ef Bull once takes a holt, heaven and yarth can't make him let go."

After Ralph's first day on the job goes poorly, ending with the feeling that he "was not of himself, and consequently not master of anybody else," he spends most of the night restless. When he thinks of how Bull acted during the hunt, however, he is hit with a new inspiration and decides that the model for his behavior as a school master should be a fierce and powerful bulldog. The quote below shows the moment of his decision:

He thought that what Flat Creek needed was a bulldog. He would be a bulldog, quiet, but invincible. He would take hold in such a way that nothing should make him let go.