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: Haloperidol ( 1 mg / kg ip ) induced parkinsonian - like muscle rigidity , measured as an increased resistance of a rat ' s hind foot to passive flexion and extension at the ankle joint .
### Output Text:
<span class="chemical">Haloperidol</span> ( 1 mg / kg ip ) induced parkinsonian - like muscle rigidity , measured as an increased resistance of a rat ' s hind foot to passive flexion and extension at the ankle joint . 