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: Frequency and severity of subjective adverse effects were also reduced after HDS : tremor ( p less than 0 . 001 ) , palpitations ( p less than 0 . 001 ) . ( ABSTRACT TRUNCATED AT 250 WORDS )
### Output Text:
Frequency and severity of subjective adverse effects were also reduced after HDS : tremor ( p less than 0 . 001 ) , palpitations ( p less than 0 . 001 ) . ( ABSTRACT TRUNCATED AT 250 WORDS ) 