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: Male Sprague - Dawley rats were injected with saline on postnatal day ( P ) 20 , or a convulsant dose of pilocarpine on P20 or P45 .
### Output Text:
Male Sprague - Dawley rats were injected with saline on postnatal day ( P ) 20 , or a convulsant dose of <span class="chemical">pilocarpine</span> on P20 or P45 . 