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: Ten patients with acute transmural myocardial infarctions received intravenous nitroglycerin , sufficient to reduce mean arterial pressure from 107 + / - 6 to 85 + / - 6 mm Hg ( P less than 0 . 001 ) , for 60 minutes .
### Output Text:
Ten patients with acute transmural myocardial infarctions received intravenous <span class="chemical">nitroglycerin</span> , sufficient to reduce mean arterial pressure from 107 + / - 6 to 85 + / - 6 mm Hg ( P less than 0 . 001 ) , for 60 minutes . 