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: Analysis of in vivo myocardial excitability , contractility , and metabolic characteristics at 16 months revealed other significant barium - induced disturbances within the cardiovascular system .
### Output Text:
Analysis of in vivo myocardial excitability , contractility , and metabolic characteristics at 16 months revealed other significant <span class="chemical">barium</span> - induced disturbances within the cardiovascular system . 