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: Their cardiac tissues were processed for light microscopy , after which cardiomyocyte damage was evaluated according to Billingham ( in Cancer Treat Rep 62 ( 6 ) : 865 - 872 , 1978 ) .
### Output Text:
Their cardiac tissues were processed for light microscopy , after which cardiomyocyte damage was evaluated according to Billingham ( in Cancer Treat Rep 62 ( 6 ) : 865 - 872 , 1978 ) . 