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: Other side effects were rare , and peripheral neurotoxicity has been minor ( 26 % grade 1 ) .
### Output Text:
Other side effects were rare , and peripheral neurotoxicity has been minor ( 26 % grade 1 ) . 