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 memory - enhancing effects of PREGS and its analogs were tested in the passive avoidance task using the model of scopolamine - induced amnesia .
### Output Text:
The memory - enhancing effects of <span class="chemical">PREGS</span> and its analogs were tested in the passive avoidance task using the model of <span class="chemical">scopolamine</span> - induced amnesia . 