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: Resting forearm vascular resistance remained unchanged , but the reflex response to the cold pressor test was accentuated , the rise in resistance increasing from 10 . 5 mm Hg / ml / 100 ml / min ( R units ) before treatment to 32 . 6 R units after treatment ( SED + / - 6 . 4 , p less than 0 . 025 ) .
### Output Text:
Resting forearm vascular resistance remained unchanged , but the reflex response to the cold pressor test was accentuated , the rise in resistance increasing from 10 . 5 mm Hg / ml / 100 ml / min ( R units ) before treatment to 32 . 6 R units after treatment ( SED + / - 6 . 4 , p less than 0 . 025 ) . 