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: Effects of active constituents of Crocus sativus L . , crocin on streptozocin - induced model of sporadic Alzheimer ' s disease in male rats .
### Output Text:
Effects of active constituents of Crocus sativus L . , <span class="chemical">crocin</span> on <span class="chemical">streptozocin</span> - induced model of sporadic Alzheimer ' s disease in male rats . 