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 pilocarpine ( PILO ) model of epilepsy is characterized by an acute period of status epilepticus followed by spontaneous recurrent seizures and related brain damage .
### Output Text:
The <span class="chemical">pilocarpine</span> ( <span class="chemical">PILO</span> ) model of epilepsy is characterized by an acute period of status epilepticus followed by spontaneous recurrent seizures and related brain damage . 