2375. A 5-year-old Jack Russell trembles continuously during the past 3 days.

What is the cause?  Poisoning of the brain?
The only history is that the owner had applied some herbal cream onto the right fore wrist to cure an open wound and the dog licked off the cream. This went on for 2 months. In the past 3 days, the dog developed the fine tremors of the body, esp. noticeable in the hind legs.

X Rays