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: In a microdialysis study , 10 muL of saline ( group C ; n = 8 ) or 30 mug of morphine ( group M ; n = 8 ) was injected intrathecally ( IT ) 0 . 5 h after reflow , and 30 mug of morphine ( group SM ; n = 8 ) or 10 muL of saline ( group SC ; n = 8 ) was injected IT 0 . 5 h after sham operation .
### Output Text:
In a microdialysis study , 10 muL of saline ( group C ; n = 8 ) or 30 mug of <span class="chemical">morphine</span> ( group M ; n = 8 ) was injected intrathecally ( IT ) 0 . 5 h after reflow , and 30 mug of <span class="chemical">morphine</span> ( group SM ; n = 8 ) or 10 muL of saline ( group SC ; n = 8 ) was injected IT 0 . 5 h after sham operation . 