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: Chronic carbamazepine treatment in the rat : efficacy , toxicity , and effect on plasma and tissue folate concentrations .
### Output Text:
Chronic <span class="chemical">carbamazepine</span> treatment in the rat : efficacy , toxicity , and effect on plasma and tissue <span class="chemical">folate</span> concentrations . 