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: This study indicates that with stable halothane anesthesia , the partial recovery of blood pressure during SNP infusion and the post - SNP rebound of blood pressure can be completely blocked by saralasin .
### Output Text:
This study indicates that with stable <span class="chemical">halothane</span> anesthesia , the partial recovery of blood pressure during <span class="chemical">SNP</span> infusion and the post - <span class="chemical">SNP</span> rebound of blood pressure can be completely blocked by <span class="chemical">saralasin</span> . 