Why does Jurgis begin to drink? What happens to him to make him fight the urge?

"Jurgis, being a man, had troubles of his own. There was another specter following him. He had never spoken of it, nor would he allow any one else to speak of it--he had never acknowledged its existence to himself. Yet the battle with it took all the manhood that he had-- and once or twice, alas, a little more. Jurgis had discovered drink.

He was working in the steaming pit of hell; day after day, week after week--until now, there was not an organ of his body that did its work without pain, until the sound of ocean breakers echoed in his head day and night, and the buildings swayed and danced before him as he went down the street. And from all the unending horror of this there was a respite, a deliverance--he could drink! He could forget the pain, he could slip off the burden; he would see clearly again, he would be master of his brain, of his thoughts, of his will. His dead self would stir in him, and he would find himself laughing and cracking jokes with his companions--he would be a man again, and master of his life.

It was not an easy thing for Jurgis to take more than two or three drinks. With the first drink he could eat a meal, and he could persuade himself that that was economy; with the second he could eat another meal--but there would come a time when he could eat no more, and then to pay for a drink was an unthinkable extravagance, a defiance of the agelong instincts of his hunger-haunted class. One day, however, he took the plunge, and drank up all that he had in his pockets, and went home half "piped," as the men phrase it. He was happier than he had been in a year; and yet, because he knew that the happiness would not last, he was savage, too with those who would wreck it, and with the world, and with his life; and then again, beneath this, he was sick with the shame of himself. Afterward, when he saw the despair of his family, and reckoned up the money he had spent, the tears came into his eyes, and he began the long battle with the specter.

It was a battle that had no end, that never could have one. But Jurgis did not realize that very clearly; he was not given much time for reflection. He simply knew that he was always fighting. Steeped in misery and despair as he was, merely to walk down the street was to be put upon the rack. There was surely a saloon on the corner-- perhaps on all four corners, and some in the middle of the block as well; and each one stretched out a hand to him each one had a personality of its own, allurements unlike any other. Going and coming--before sunrise and after dark--there was warmth and a glow of light, and the steam of hot food,and perhaps music, or a friendly face, and a word of good cheer. Jurgis developed a fondness for having Ona on his arm whenever he went out on the street, and he would hold her tightly, and walk fast. It was pitiful to have Ona know of this--it drove him wild to think of it; the thing was not fair, for Ona had never tasted drink, and so could not understand. Sometimes, in despeate hours, he would find himself wishing that she might learn what it was, so that he need not be ashamed in her presence. They might drink together, and escape from the horror-- escape for a while, come what would."