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: Fifteen days later , the lesioned group still showed values significantly lower than the sham group ( 150 + / - 6 versus 167 + / - 5 mm Hg , p less than 0 . 05 ) .
### Output Text:
Fifteen days later , the lesioned group still showed values significantly lower than the sham group ( 150 + / - 6 versus 167 + / - 5 mm Hg , p less than 0 . 05 ) . 