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: Patients who are unusually sensitive to the neuromuscular effects of magnesium should be suspected of having an underlying disorder of neuromuscular transmission .
### Output Text:
Patients who are unusually sensitive to the neuromuscular effects of <span class="chemical">magnesium</span> should be suspected of having an underlying disorder of neuromuscular transmission . 