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: CONCLUSION : Therefore , these results demonstrate the effectiveness of crocin ( 30 mg / kg ) in antagonizing the cognitive deficits caused by STZ - icv in rats and its potential in the treatment of neurodegenerative diseases such as Alzheimer ' s disease .
### Output Text:
CONCLUSION : Therefore , these results demonstrate the effectiveness of <span class="chemical">crocin</span> ( 30 mg / kg ) in antagonizing the cognitive deficits caused by <span class="chemical">STZ</span> - icv in rats and its potential in the treatment of neurodegenerative diseases such as Alzheimer ' s disease . 