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 same experimental conditions , PG - 9 ( 5 - 20 microg per mouse , i . c . v . ) was also able to prevent antimuscarine - induced amnesia , demonstrating a central localization of the activity .
### Output Text:
In the same experimental conditions , <span class="chemical">PG - 9</span> ( 5 - 20 microg per mouse , i . c . v . ) was also able to prevent antimuscarine - induced amnesia , demonstrating a central localization of the activity . 