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: These experimental findings represent the first indication that life - long barium ingestion may have significant adverse effects on the mammalian cardiovascular system .
### Output Text:
These experimental findings represent the first indication that life - long <span class="chemical">barium</span> ingestion may have significant adverse effects on the mammalian cardiovascular system . 