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: Individual symptoms , total symptoms , and major symptoms were compared to determine efficacy of medication .
### Output Text:
Individual symptoms , total symptoms , and major symptoms were compared to determine efficacy of medication . 