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: The mechanism of CS protection does not appear to be dependent on the inhibition of chemical bioactivation to a toxic reactive intermediate ( in light of the protection observed against galactosamine hepatotoxicity ) .
### Output Text:
The mechanism of <span class="chemical">CS</span> protection does not appear to be dependent on the inhibition of chemical bioactivation to a toxic reactive intermediate ( in light of the protection observed against <span class="chemical">galactosamine</span> hepatotoxicity ) . 