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: Total blindness with a transient tonic pupillary response , denervation supersensitivity , and abnormal visual - evoked potentials developed in a 54 - year - old man after the use of quinine sulfate for leg cramps .
### Output Text:
Total blindness with a transient tonic pupillary response , denervation supersensitivity , and abnormal visual - evoked potentials developed in a 54 - year - old man after the use of <span class="chemical">quinine sulfate</span> for leg cramps . 