In cirque du freak how does Darren turn into a vampire?

*Warning, Spoilers*

Darren Shan gets tickets to go see a show called Cirque du Freak, a freak show. When he is there, he watches Mr. Crepsley, who Darren later finds out he is a vampire, perform with his spider, Madam Octa. Darren, being obbessed with Spiders and all, wants her. A few days after the show is over he goes back to the old theater where the freak show had played and steals the spider and brings it home with him. Then, his friend Steve comes over and they do tricks with the spider. But then Madam Octa bites Steve, but it doesn't kill him, it only paralyzes him. Darren goes to Mr. Crepsley and asks for an antidote for the poisoning. Mr. Crepsley gives him the antidote, but Darren has to become a half vampire and his assistant. Mr. Crepsley cuts the tips of his and Darren's fingers. They press their hands together, letting eachother's blood flow into them. They hold it there for a few seconds, exchanging blood. Then he is a vampire.

Long enough for ya? ;)