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: All the animals treated with tacrine - loaded nanoparticles showed an earlier outcome of CNS adverse symptoms , i . e . epileptic onset , with respect to those animals treated with the free compound ( 10 min vs . 22 min respectively ) .
### Output Text:
All the animals treated with <span class="chemical">tacrine</span> - loaded nanoparticles showed an earlier outcome of CNS adverse symptoms , i . e . epileptic onset , with respect to those animals treated with the free compound ( 10 min vs . 22 min respectively ) . 