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: OBJECTIVE : To examine the effects of dehydroepiandrosterone ( DHEA ) on animal models of schizophrenia .
### Output Text:
OBJECTIVE : To examine the effects of <span class="chemical">dehydroepiandrosterone</span> ( <span class="chemical">DHEA</span> ) on animal models of schizophrenia . 