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: Treatment for scabies is usually initiated by general practitioners ; most consider lindane ( gamma benzene hexachloride ) the treatment of choice .
### Output Text:
Treatment for scabies is usually initiated by general practitioners ; most consider <span class="chemical">lindane</span> ( <span class="chemical">gamma benzene hexachloride</span> ) the treatment of choice . 