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: Latency to the loss of righting reflex , rigidity and behavior on recovery , reflected the relative predominance of ketamine or morphine in each combination .
### Output Text:
Latency to the loss of righting reflex , rigidity and behavior on recovery , reflected the relative predominance of <span class="chemical">ketamine</span> or <span class="chemical">morphine</span> in each combination . 