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: A survey of 15 independent inbred strains of mice revealed that ventricular cardiomyocyte nuclear number ranged from 3 to 13 % mononucleate , suggesting that cardiomyocyte terminal differentiation is influenced directly or indirectly by genetic background .
### Output Text:
A survey of 15 independent inbred strains of mice revealed that ventricular cardiomyocyte nuclear number ranged from 3 to 13 % mononucleate , suggesting that cardiomyocyte terminal differentiation is influenced directly or indirectly by genetic background . 