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: Ginsenoside Rg1 restores the impairment of learning induced by chronic morphine administration in rats .
### Output Text:
<span class="chemical">Ginsenoside Rg1</span> restores the impairment of learning induced by chronic <span class="chemical">morphine</span> administration in rats . 