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: One day after experimental myocardial infarction , six additional halothane - anesthetized dogs received 4 micrograms . kg - 1 . min - 1 epinephrine until VT appeared .
### Output Text:
One day after experimental myocardial infarction , six additional <span class="chemical">halothane</span> - anesthetized dogs received 4 micrograms . kg - 1 . min - 1 <span class="chemical">epinephrine</span> until VT appeared . 