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 inhibitory effect of carteolol was almost comparable to that of propranolol , but was weaker than that of biperiden .
### Output Text:
The inhibitory effect of <span class="chemical">carteolol</span> was almost comparable to that of <span class="chemical">propranolol</span> , but was weaker than that of <span class="chemical">biperiden</span> . 