Just thought I'd add my experience.
 
I had a ferret that had become ill.  She was lethargic, losing weight, and
grinding her teeth.  I brought her to the vet, but they couldn't figure it
out and at the time I didn't know much about ferrets.  They told me to take
her home and keep an eye on her.  I brought her back about a week later
because she wasn't getting any better.  They took radiographs, did an
ultrasound and finally drew some blood.  Radiographs were normal, ultrasound
revealed a mass behind the liver -- but they thought it might be the spleen
because they couldn't find it.  Unfortunately, when they took a blood
sample, her blood was almost like water.  Her PCV (packed cell volume) was
less than 10%.  I decided to have her euthanized.  At necropsy they found a
ruptured gastric ulcer with severe peritonitis.  If caught early enough and
treated, perhaps tragedy can be prevented.
 
                                Lisa, Daisy and Squirt
[Posted in FML issue 1629]