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 aim was to evaluate the effects of high frequency hippocampal stimulation on cortical epileptic activity in penicillin - induced epilepsy model .
### Output Text:
The aim was to evaluate the effects of high frequency hippocampal stimulation on cortical epileptic activity in <span class="chemical">penicillin</span> - induced epilepsy model . 