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 effect of nitroglycerin on heart rate and systolic blood pressure was compared in 5 normal subjects , 12 diabetic subjects without autonomic neuropathy , and 5 diabetic subjects with autonomic neuropathy .
### Output Text:
The effect of <span class="chemical">nitroglycerin</span> on heart rate and systolic blood pressure was compared in 5 normal subjects , 12 diabetic subjects without autonomic neuropathy , and 5 diabetic subjects with autonomic neuropathy . 