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: Adrenaline arrhythmia , which is suppressed by Ca channel blockers , was induced by adrenaline infusion in halothane - anesthetized dogs .
### Output Text:
Adrenaline arrhythmia , which is suppressed by <span class="chemical">Ca</span> channel blockers , was induced by <span class="chemical">adrenaline</span> infusion in <span class="chemical">halothane</span> - anesthetized dogs . 