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: Steroid treatment also induced a leftward shift of the force - frequency curve at 25 and 50 Hz when compared with saline treatment ( p < 0 . 05 ) .
### Output Text:
<span class="chemical">Steroid</span> treatment also induced a leftward shift of the force - frequency curve at 25 and 50 Hz when compared with saline treatment ( p < 0 . 05 ) . 