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 1 - yr mortality was significantly higher after aprotinin treatment in the high risk surgery group ( 17 . 7 % vs 9 . 8 % , P = 0 . 034 ) .
### Output Text:
The 1 - yr mortality was significantly higher after aprotinin treatment in the high risk surgery group ( 17 . 7 % vs 9 . 8 % , P = 0 . 034 ) . 