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: Our report emphasizes the need for monitoring of visual function in patients on long - term linezolid treatment .
### Output Text:
Our report emphasizes the need for monitoring of visual function in patients on long - term <span class="chemical">linezolid</span> treatment . 