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: No histopathological alterations or differences in bone formation were seen in the limbs or toes of any chicks from any group ; however , extensive cranial hemorrhage occurred in all nicotine sulfate - treated chicks .
### Output Text:
No histopathological alterations or differences in bone formation were seen in the limbs or toes of any chicks from any group ; however , extensive cranial hemorrhage occurred in all <span class="chemical">nicotine</span> sulfate - treated chicks . 