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: These results demonstrate that , in these experimental conditions , DXNP killed less animals than free DX , despite of an enhanced renal toxicity of the former .
### Output Text:
These results demonstrate that , in these experimental conditions , DXNP killed less animals than free <span class="chemical">DX</span> , despite of an enhanced renal toxicity of the former . 