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: Both isomers of propranolol were capable of preventing adrenaline - induced cardiac arrhythmias in cats anaesthetized with halothane , but the mean dose of ( - ) - propranolol was 0 . 09 + / - 0 . 02 mg / kg whereas that of ( + ) - propranolol was 4 . 2 + / - 1 . 2 mg / kg .
### Output Text:
Both isomers of <span class="chemical">propranolol</span> were capable of preventing <span class="chemical">adrenaline</span> - induced cardiac arrhythmias in cats anaesthetized with <span class="chemical">halothane</span> , but the mean dose of ( - ) - <span class="chemical">propranolol</span> was 0 . 09 + / - 0 . 02 mg / kg whereas that of ( + ) - <span class="chemical">propranolol</span> was 4 . 2 + / - 1 . 2 mg / kg . 