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: Peripheral neuropathy was common ( 63 % ) , but severe grade 3 - 4 peripheral neuropathy was not observed .
### Output Text:
Peripheral neuropathy was common ( 63 % ) , but severe grade 3 - 4 peripheral neuropathy was not observed . 