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: As a result , routine plasma screening would yield few cases of stimulant drug in which there was neither a history nor suspicion of drug abuse in this population .
### Output Text:
As a result , routine plasma screening would yield few cases of stimulant drug in which there was neither a history nor suspicion of drug abuse in this population . 