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: Neither SOD nor DMTU affected the renal cortical GM content in GM - treated rats .
### Output Text:
Neither SOD nor <span class="chemical">DMTU</span> affected the renal cortical <span class="chemical">GM</span> content in <span class="chemical">GM</span> - treated rats . 