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: In the present study we aimed to portray a detailed spectral analysis of penicillin - induced epileptiform activity in comparison with basal brain activity in anesthetized Wistar rats .
### Output Text:
In the present study we aimed to portray a detailed spectral analysis of <span class="chemical">penicillin</span> - induced epileptiform activity in comparison with basal brain activity in anesthetized Wistar rats . 