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: Thirty - six iopentol injections , 35 iohexol injections and 37 metrizoate injections were made .
### Output Text:
Thirty - six <span class="chemical">iopentol</span> injections , 35 <span class="chemical">iohexol</span> injections and 37 <span class="chemical">metrizoate</span> injections were made . 