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: The most striking effect was sedation which increased with the dose , 2 mg producing deep sleep although the subjects could still be aroused .
### Output Text:
The most striking effect was sedation which increased with the dose , 2 mg producing deep sleep although the subjects could still be aroused . 