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: At the highest effective doses , PG - 9 did not produce any collateral symptoms as revealed by the Irwin test , and it did not modify spontaneous motility and inspection activity , as revealed by the hole - board test .
### Output Text:
At the highest effective doses , <span class="chemical">PG - 9</span> did not produce any collateral symptoms as revealed by the Irwin test , and it did not modify spontaneous motility and inspection activity , as revealed by the hole - board test . 