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: METHODS : The present experiments explored whether azathioprine influences eryptosis .
### Output Text:
METHODS : The present experiments explored whether <span class="chemical">azathioprine</span> influences eryptosis . 