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: By way of contrast , mice treated with daidzein prior to the scopolamine injections were noticeably protected from this performance impairment ( an approximately 12 % - 21 % decrease in alternation behavior ) .
### Output Text:
By way of contrast , mice treated with <span class="chemical">daidzein</span> prior to the <span class="chemical">scopolamine</span> injections were noticeably protected from this performance impairment ( an approximately 12 % - 21 % decrease in alternation behavior ) . 