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 should be warned about the side effects of vertigo and vomiting , which subsides gradually with every new instillation , and that the tinnitus may not disappear but will be alleviated , enabling them to cope more easily with the disease and lead a more normal life .
### Output Text:
Patients should be warned about the side effects of vertigo and vomiting , which subsides gradually with every new instillation , and that the tinnitus may not disappear but will be alleviated , enabling them to cope more easily with the disease and lead a more normal life . 