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: The cardiotoxic effects of adriamycin were studied in mammalian myocardial cells in culture as a model system .
### Output Text:
The cardiotoxic effects of <span class="chemical">adriamycin</span> were studied in mammalian myocardial cells in culture as a model system . 