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: After a short period of basal activity recording , epileptic focus was induced by injecting 400IU / 2 microl penicillin - G potassium into the left lateral ventricle while the cortical activity was continuously recorded .
### Output Text:
After a short period of basal activity recording , epileptic focus was induced by injecting 400IU / 2 microl <span class="chemical">penicillin - G potassium</span> into the left lateral ventricle while the cortical activity was continuously recorded . 