Introducing a baby rat to an adult.

Question
Hey there! I have had a male rat called Merlin living on his own since I got him, he is now 2 years old and I decided to get another male rat to perhaps look after Merlin in his old age.  The new male is called Doofus and he is little over 7 weeks old.  I've been trying to introduce them using advised techniques and at first it seemed Merlin didn't mind Doofus too much. I popped them in the bathtub and at first Merlin flipped Doofus over and pinned him down and then Merlin kept nearly lying down letting Doofus have a sniff.  They were okay for half an hour and so I took them into the bedroom and put them on the bed. Again, they seemed okay together and then Merlin kept curling his body towards Doofus and kinda got him in a corner. Doofus kept squeeling a lot and so I removed him.  Later on I got Doofus and put him on my lap but Merlin kept swiping him with his front poor and kept blocking Doofus in a corner again.  I've tried a few times but Merlin still behaves this way.  Everytime I've tried to introduce them I have smeared vanilla extract onto them and Merlin has never been an agressive rat.  I have also put them in each other's cages for a few hours.  I'm not sure what to do next, I'm running out of ideas. Help!

Answer
I think the first problem you ran into is that you kept changing their location. Once the introduction is done on a neutral territory, I leave them in that territory until their cage is completely done and sanitized.. once the cage is ready for them, they go in the cage and are ignored by me (in a sense - I keep an ear out for arguing) for the rest of the night. Although squealing, pinning, and random acts of dominance SEEM aggressive, really its a very natural part of the process and the rule of thumb with rats is NO BLOOD, NO FOUL. So unless Merlin is trying to shred your little guy, leave them alone and let them work it out. Seems harsh, but it has to happen. Every time you break it up, you in turn make the situation worse, and Merlin has to re-assert himself.