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: METHOD : The sample for the study consisted of 50 patients to whom subcutaneous heparin was administered .
### Output Text:
METHOD : The sample for the study consisted of 50 patients to whom subcutaneous <span class="chemical">heparin</span> was administered . 