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: Ritanserin - treated rats ( 4 microg / 0 . 5 microl / side ) showed a significant decrease in the mentioned parameters as compared to DMSO - treated group .
### Output Text:
<span class="chemical">Ritanserin</span> - treated rats ( 4 microg / 0 . 5 microl / side ) showed a significant decrease in the mentioned parameters as compared to <span class="chemical">DMSO</span> - treated group . 