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: IFO and Mesna were administrated separately on rabbit ' s lymphocytes in vivo , which were later developed in vitro .
### Output Text:
<span class="chemical">IFO</span> and <span class="chemical">Mesna</span> were administrated separately on rabbit ' s lymphocytes in vivo , which were later developed in vitro . 