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: Ninety - six Swiss - Webster mice ( 30 - 35 g , 6 - 8 wk ) , were randomized into 6 groups 1 ) saline ( control ) , 2 ) NTG immediately after learning , 3 ) NTG 3 h after learning , 4 ) NTG and NIMO , 5 ) vehicle , and 6 ) NIMO alone .
### Output Text:
Ninety - six Swiss - Webster mice ( 30 - 35 g , 6 - 8 wk ) , were randomized into 6 groups 1 ) saline ( control ) , 2 ) <span class="chemical">NTG</span> immediately after learning , 3 ) <span class="chemical">NTG</span> 3 h after learning , 4 ) <span class="chemical">NTG</span> and <span class="chemical">NIMO</span> , 5 ) vehicle , and 6 ) <span class="chemical">NIMO</span> alone . 