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: There was also a higher incidence of tachyarrhythmias ( P less than 0 . 05 ) and ventricular ectopic beats ( P less than 0 . 05 ) in the morphine infusion group .
### Output Text:
There was also a higher incidence of tachyarrhythmias ( P less than 0 . 05 ) and ventricular ectopic beats ( P less than 0 . 05 ) in the <span class="chemical">morphine</span> infusion group . 