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: In order to conduct reliable testing in this regard , it is essential that a positive control for induction be available .
### Output Text:
In order to conduct reliable testing in this regard , it is essential that a positive control for induction be available . 