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: Further , in experiment set up 2 : where memory function was not affected i . e . 7 - 9 days after STZ treatment .
### Output Text:
Further , in experiment set up 2 : where memory function was not affected i . e . 7 - 9 days after <span class="chemical">STZ</span> treatment . 