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: Kanamycin and netilmicin appeared to have no effect at the dose used .
### Output Text:
<span class="chemical">Kanamycin</span> and <span class="chemical">netilmicin</span> appeared to have no effect at the dose used . 