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: Depletion of sulfhydryl ( SH ) groups has been reported from cell culture , animal and clinical studies .
### Output Text:
Depletion of <span class="chemical">sulfhydryl</span> ( <span class="chemical">SH</span> ) groups has been reported from cell culture , animal and clinical studies . 