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: Atherosclerosis could produce gastric hemorrhagic ulcer via aggravation of gastric acid back - diffusion , LPO generation , histamine release and microvascular permeability that could be ameliorated by verapamil in rats .
### Output Text:
Atherosclerosis could produce gastric hemorrhagic ulcer via aggravation of gastric acid back - diffusion , LPO generation , <span class="chemical">histamine</span> release and microvascular permeability that could be ameliorated by <span class="chemical">verapamil</span> in rats . 