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: Brain injury ( percentage of the ischemic hemisphere ) was less in the 15 / HTN group ( 16 + / - 6 , mean + / - SD ) versus the 90 / HTN group ( 30 + / - 6 ) , which was in turn less than the control group ( 42 + / - 5 ) .
### Output Text:
Brain injury ( percentage of the ischemic hemisphere ) was less in the 15 / HTN group ( 16 + / - 6 , mean + / - SD ) versus the 90 / HTN group ( 30 + / - 6 ) , which was in turn less than the control group ( 42 + / - 5 ) . 