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: METHODS : Marmosets were administered 1 - methyl - 4 - phenyl - 1 , 2 , 3 , 6 - tetrahydropyridine ( 2 . 0 mg / kg s . c . ) for five days , resulting in stable parkinsonism .
### Output Text:
METHODS : Marmosets were administered <span class="chemical">1 - methyl - 4 - phenyl - 1 , 2 , 3 , 6 - tetrahydropyridine</span> ( 2 . 0 mg / kg s . c . ) for five days , resulting in stable parkinsonism . 