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: Tolerability was assessed by monitoring adverse events at randomization and all subsequent study visits and regular evaluation of hematology and blood chemistry .
### Output Text:
Tolerability was assessed by monitoring adverse events at randomization and all subsequent study visits and regular evaluation of hematology and blood chemistry . 