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: Effects of the hippocampal deep brain stimulation on cortical epileptic discharges in penicillin - induced epilepsy model in rats .
### Output Text:
Effects of the hippocampal deep brain stimulation on cortical epileptic discharges in <span class="chemical">penicillin</span> - induced epilepsy model in rats . 