| If it is Canker...
It is infectious, so keep strict hygene procedures. Best to get it too a vet, it will probably need antibiotic treatment, possibly multiple injections. Also get it on some good heat, at least 35 degees if not a bit more, and take any water out of the encolsure to reduce the humidity. give fresh bowl of water every day for 5 to 10 minutes, to allow it to drink. Also wipe out the inside of the mouth around the puss area to keep it clean, using cotton buds.
And... get it to a vet! JMO | 
