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: Intraperitoneal administration of atropine , naloxone , mecamylamine , and hexamethonium to mice reduced catalepsy induced by a combination of morphine with nicotine .
### Output Text:
Intraperitoneal administration of <span class="chemical">atropine</span> , <span class="chemical">naloxone</span> , <span class="chemical">mecamylamine</span> , and <span class="chemical">hexamethonium</span> to mice reduced catalepsy induced by a combination of <span class="chemical">morphine</span> with <span class="chemical">nicotine</span> . 