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: Hematologic toxicities were mild : only one patient ( 2 % ) developed grade 3 or 4 neutropenia , while 29 % had grade 1 or 2 .
### Output Text:
Hematologic toxicities were mild : only one patient ( 2 % ) developed grade 3 or 4 neutropenia , while 29 % had grade 1 or 2 . 