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 heart rate in these animals was approximately 12 % lower than that measured in age - matched control rats ( P less than 0 . 05 ) .
### Output Text:
The heart rate in these animals was approximately 12 % lower than that measured in age - matched control rats ( P less than 0 . 05 ) . 