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: The pressor response to i . c . carbachol ( 1 mug ) remained unchanged after sectioning of the bilateral cervical vagal nerves but disappeared after sectioning of the spinal cord ( C7 - C8 ) .
### Output Text:
The pressor response to i . c . <span class="chemical">carbachol</span> ( 1 mug ) remained unchanged after sectioning of the bilateral cervical vagal nerves but disappeared after sectioning of the spinal cord ( C7 - C8 ) . 