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: Vincristine , dexamethasone , and polyethylene glycol - asparaginase were also administered before the episode as part of induction therapy .
### Output Text:
<span class="chemical">Vincristine</span> , <span class="chemical">dexamethasone</span> , and <span class="chemical">polyethylene glycol - asparaginase</span> were also administered before the episode as part of induction therapy . 