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: Melatonin 0 . 5 and 5 mg / kg influenced the duration but not the latency of ketamine - or diazepam - induced narcosis .
### Output Text:
<span class="chemical">Melatonin</span> 0 . 5 and 5 mg / kg influenced the duration but not the latency of <span class="chemical">ketamine</span> - or <span class="chemical">diazepam</span> - induced narcosis . 