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: Drug - induced liver injury : an analysis of 461 incidences submitted to the Spanish registry over a 10 - year period .
### Output Text:
Drug - induced liver injury : an analysis of 461 incidences submitted to the Spanish registry over a 10 - year period . 