On the Road Part 4, Chapter 4
As they drive, a bug stings Stan and his arm starts to swell badly. They are a little shaken but they continue to drive, hoping the swelling will stop, but it only gets worse. They tell him they'll stop at the first hospital they find.
They keep driving and tell each other stories of their youth and their experiences. They arrive in New Mexico near Texas, where Sal had been before, and continue to drive through the night. Dean and Sal tell book plots to Stan. Dean doesn't care at all about Texas, so Sal drives while he sleeps in the back. Stan talks a lot about England and France. A wave of heat descends as they enter San Antonio, a city that Sal says must look like Mexico. They drink and get high and decide to stop at a hospital for Stan:
"The hospital was full of poor Mexican women, some of them pregnant, some of them sick or brining their little sick kiddies. It was sad. I thought of poor Terry and wondered what she was doing now." Part 4, Chapter 4, pg. 272
Stan gets a shot of penicillin. Meanwhile, Dean is amazed with San Antonio. He loves the city, the women, and everything else. Dean is eager to get to Mexico, and they are only 150 miles from the border. Sal sleeps for awhile and wakes at the end of Texas--Laredo. The town is sinister. They roll into Mexico and it is exactly as they imagined it. They change their money to pesos.