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: Third , although it is relatively easy to block seizures induced by lithium and pilocarpine by administration of anticonvulsants prior to pilocarpine , it is more difficult to terminate ongoing status epilepticus and block the lethality of the seizures .
### Output Text:
Third , although it is relatively easy to block seizures induced by <span class="chemical">lithium</span> and <span class="chemical">pilocarpine</span> by administration of anticonvulsants prior to <span class="chemical">pilocarpine</span> , it is more difficult to terminate ongoing status epilepticus and block the lethality of the seizures . 