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: After atropine the CD25 was unchanged after placebo ( 2 . 3 + / - 0 . 3 micrograms ) and atenolol ( 7 . 7 + / - 1 . 3 micrograms ) ; it was reduced after propranolol ( 24 . 8 + / - 5 . 0 micrograms ) , but remained different from atenolol .
### Output Text:
After <span class="chemical">atropine</span> the CD25 was unchanged after placebo ( 2 . 3 + / - 0 . 3 micrograms ) and <span class="chemical">atenolol</span> ( 7 . 7 + / - 1 . 3 micrograms ) ; it was reduced after <span class="chemical">propranolol</span> ( 24 . 8 + / - 5 . 0 micrograms ) , but remained different from <span class="chemical">atenolol</span> . 