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: They received morphine in doses of 32 micrograms / kg / hr and 40 micrograms / kg / hr larger than a group of 10 neonates who received 6 - 24 micrograms / kg / hr and had no seizures .
### Output Text:
They received <span class="chemical">morphine</span> in doses of 32 micrograms / kg / hr and 40 micrograms / kg / hr larger than a group of 10 neonates who received 6 - 24 micrograms / kg / hr and had no seizures . 