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: Our data suggested that the ginsenoside Re , but not Rg1 or Rb1 , may contribute toward reversal of OIH .
### Output Text:
Our data suggested that the <span class="chemical">ginsenoside Re</span> , but not <span class="chemical">Rg1</span> or <span class="chemical">Rb1</span> , may contribute toward reversal of OIH . 