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: This change with propranolol sensitivity was calculated as the apparent Ka , this was unchanged by atropine ( 11 . 7 + / - 2 . 1 and 10 . 1 + / - 2 . 5 ml / ng ) .
### Output Text:
This change with <span class="chemical">propranolol</span> sensitivity was calculated as the apparent Ka , this was unchanged by <span class="chemical">atropine</span> ( 11 . 7 + / - 2 . 1 and 10 . 1 + / - 2 . 5 ml / ng ) . 