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 findings showed that peripheral iron dextran overload increased the iron staining positive cells and reduced the number of TH - immunoreactive neurons in the SN .
### Output Text:
The findings showed that peripheral <span class="chemical">iron dextran</span> overload increased the <span class="chemical">iron</span> staining positive cells and reduced the number of TH - immunoreactive neurons in the SN . 