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: There were no appreciable differences between the MESNA series and the conventional prophylaxis series with respect to either haematological or systemic toxicity of the cytostatic treatment .
### Output Text:
There were no appreciable differences between the <span class="chemical">MESNA</span> series and the conventional prophylaxis series with respect to either haematological or systemic toxicity of the cytostatic treatment . 