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: Comparative study : Endografine ( diatrizoate ) , Vasurix polyvidone ( acetrizoate ) , Dimer - X ( iocarmate ) and Hexabrix ( ioxaglate ) in hysterosalpingography .
### Output Text:
Comparative study : <span class="chemical">Endografine</span> ( <span class="chemical">diatrizoate</span> ) , <span class="chemical">Vasurix polyvidone</span> ( <span class="chemical">acetrizoate</span> ) , <span class="chemical">Dimer - X</span> ( <span class="chemical">iocarmate</span> ) and <span class="chemical">Hexabrix</span> ( <span class="chemical">ioxaglate</span> ) in hysterosalpingography . 