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: In addition , crocin in the mentioned dose could significantly attenuated learning and memory impairment in treated STZ - injected group in passive avoidance test .
### Output Text:
In addition , <span class="chemical">crocin</span> in the mentioned dose could significantly attenuated learning and memory impairment in treated <span class="chemical">STZ</span> - injected group in passive avoidance test . 