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: They were then treated chronically with L - DOPA / benserazide 50 / 12 . 5 mg / kg given orally daily for 2 months .
### Output Text:
They were then treated chronically with <span class="chemical">L - DOPA / benserazide</span> 50 / 12 . 5 mg / kg given orally daily for 2 months . 