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: RESULTS : The percentage of bruising occurrence was 64 % with the injection of 10 seconds duration and 42 % in the 30 - second injection .
### Output Text:
RESULTS : The percentage of bruising occurrence was 64 % with the injection of 10 seconds duration and 42 % in the 30 - second injection . 