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: Twenty - six cases of Reye syndrome from The Children ' s Hospital , Camperdown , Australia , occurring between 1973 and 1982 were reviewed .
### Output Text:
Twenty - six cases of Reye syndrome from The Children ' s Hospital , Camperdown , Australia , occurring between 1973 and 1982 were reviewed . 