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: Herein , we report that multiple ( but not single ) injections of METH significantly increased aggressiveness in male CD - 1 mice .
### Output Text:
Herein , we report that multiple ( but not single ) injections of <span class="chemical">METH</span> significantly increased aggressiveness in male CD - 1 mice . 