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 behavioral studies , pretreatment of Swiss Webster mice with UMB24 or ( + / - ) - SM 21 significantly attenuated cocaine - induced convulsions and locomotor activity , but not lethality .
### Output Text:
In behavioral studies , pretreatment of Swiss Webster mice with <span class="chemical">UMB24</span> or ( + / - ) - <span class="chemical">SM 21</span> significantly attenuated <span class="chemical">cocaine</span> - induced convulsions and locomotor activity , but not lethality . 