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 : Adult male Wistar rats were intracerebroventricularly ( icv ) infused with STZ ( 750 ug ) on d 1 and d 3 , and a passive avoidance task was assessed 2 weeks after the first injection of STZ .
### Output Text:
METHODS : Adult male Wistar rats were intracerebroventricularly ( icv ) infused with <span class="chemical">STZ</span> ( 750 ug ) on d 1 and d 3 , and a passive avoidance task was assessed 2 weeks after the first injection of <span class="chemical">STZ</span> . 