First of all they should not be interacting unless the new kitty has been tested. She could have a number of different diseases and you wouldn't even know it.
Second of all, there are a lot of ways to introduce cats. I would be completely suprised if there was no hissing at all. You need to let them find each other on their own. Let them sniff, hiss, growl maybe even tussle a bit. As long as no blood is being drawn, they will need to determine who is the alpha cat. Be ready with a towel and if one of them screams or there is blood or something throw it over them and remove one of them from the area.
Give them a few days to cool down and try again.
Get some Feliway plug ins to ease the introductions.
If your cat ONLY hiss and jumped out of your arms, did he run towards the new cat or away from? Unless he immediately run up and attacked the other, they are fine. There is nothing wrong. Let them meet again. DO NOT bring one cat in above the other, they can see this as a threat. Just open the doors that seperate them and let them find each other.