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: Thirty male Sprague - Dawley rats were divided randomly into four treatment groups : saline , dexamethasone ( dex ) , allopurinol plus saline , and allopurinol plus dex .
### Output Text:
Thirty male Sprague - Dawley rats were divided randomly into four treatment groups : saline , <span class="chemical">dexamethasone</span> ( <span class="chemical">dex</span> ) , <span class="chemical">allopurinol</span> plus saline , and <span class="chemical">allopurinol</span> plus <span class="chemical">dex</span> . 