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: It is longer acting than physostigmine and is used in anaesthesia to reverse the non - depolarizing neuromuscular block .
### Output Text:
It is longer acting than <span class="chemical">physostigmine</span> and is used in anaesthesia to reverse the non - depolarizing neuromuscular block . 