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: The third group received an additional injection of diltiazem the day before and first 2 days after the contrast injection .
### Output Text:
The third group received an additional injection of <span class="chemical">diltiazem</span> the day before and first 2 days after the <span class="chemical">contrast</span> injection . 