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: There were 13 cases of adverse reactions ( 0 . 34 % ) , ten of which were mild reactions such as nausea , exanthema , urtication , itchiness , and urgency to defecate , and did not require treatment .
### Output Text:
There were 13 cases of adverse reactions ( 0 . 34 % ) , ten of which were mild reactions such as nausea , exanthema , urtication , itchiness , and urgency to defecate , and did not require treatment . 