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: CASE REPORT : Two , 3 - year - old male , identical twin siblings presented to the emergency department after found playing with a an empty bottle of pemoline originally containing 59 tablets .
### Output Text:
CASE REPORT : Two , 3 - year - old male , identical twin siblings presented to the emergency department after found playing with a an empty bottle of <span class="chemical">pemoline</span> originally containing 59 tablets . 