My pet rat, completely lost on what it could be.

Question
I came here before asking a question about one of my pet rats. It's the same one, he is a male rate and he is three years old. I've been reading for hours and I just have no idea what he has! But I'm beyond worried because I highly doubt my Ma will take him to the vet again.. well, today out of nowhere I notice his one foot was pretty bigger than the other one! It's a little bit of red, too. I read here http://answers.yahoo.com/question/index?qid=20080606140446AAuGzlw that is was just a simple thing and I could treat it myself, so I placed a wet cloth over it and just bought him some Children Mortin (I have not given him any because I am not sure what dose to give him nor how to give it to him) but than I keep reading other things that it could be bumblefoot? But I can't find any type of cut or anything on his foot! So I have no idea what to do, it looks like the ones in the pictures here http://www.freewebs.com/crittercity/swollenfootinfection.htm
But I keep reading almost everywhere (such as here for one example http://exoticpets.about.com/od/careofrats/p/bumblefoot.htm)
That it has something to do with an open wound, and I just can't find one! So I am so stuck on what to do, because if my poor baby has the bumblefoot I would be lost! I have no idea how I would even get him to the vet myself nor the money!
He has one other rat with him, same age, same sex - they are brothers. I took their bedding out awhile ago because his brother sadly got an abscesses (which is healing greatly!) and didn't want anything to bother him with it. So I have no idea how the one with the swollen foot could even get a cut or some sort of open wound! Where would the open wound be located at? What would it look like? I can take pictures of his foot if needed!
Thank you.

Answer
I am the owner of the site, Critter city, where you  found the photos of the bumblefoot.
As far as there being an open cut, this is how the bacteria first enters the body, but you cant always see the open cut like you  are thinking of.  In fact, sometimes the wound can be so tiny, the naked eye cant even see it, so its impossible to find a cut if thats what your looking for.
This is a nasty infection and MUST be treated with oral antibiotics.  Normal bumblefoot only causes inflamation locally on the bottom of the foot, but when infection gets into the foot it can go into the bone and tissue and cause what your seeing now. This can be fatal if left untreated. Any infection can be since it can travel into the blood stream and cause sepsis.   Your vet needs to be up to date on rat care in order to properly treat your rat. Print off what you have found from my website and present it to the vet. Also I can find one for you if you would like. Let me know your location.