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 the present study , the effect of crocins on sporadic Alzheimer ' s disease induced by intracerebroventricular ( icv ) streptozocin ( STZ ) in male rats was investigated .
### Output Text:
In the present study , the effect of <span class="chemical">crocins</span> on sporadic Alzheimer ' s disease induced by intracerebroventricular ( icv ) <span class="chemical">streptozocin</span> ( <span class="chemical">STZ</span> ) in male rats was investigated . 