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: Differential effects of non - steroidal anti - inflammatory drugs on seizures produced by pilocarpine in rats .
### Output Text:
Differential effects of non - steroidal anti - inflammatory drugs on seizures produced by <span class="chemical">pilocarpine</span> in rats . 