In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: In our case the therapy with zinc acetate represented an effective treatment for a Wilson ' s disease patient in which penicillamine - related side effects appeared .
### Output Text:
In our case the therapy with <span class="chemical">zinc acetate</span> represented an effective treatment for a Wilson ' s disease patient in which <span class="chemical">penicillamine</span> - related side effects appeared . 