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: Cognitive function testing was performed before dosing and over a 24 - hour period after dosing on Days 1 , 2 , and 25 .
### Output Text:
Cognitive function testing was performed before dosing and over a 24 - hour period after dosing on Days 1 , 2 , and 25 . 