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: The aorta / serum - ratio and the radioactive build - up 24 and 48 hours after injection of 131I - HSA was reduced in animals treated with D - pen for 42 days , indicating an impeded transmural transport of tracer which may be caused by a steric exclusion effect of abundant hyaluronate .
### Output Text:
The aorta / serum - ratio and the radioactive build - up 24 and 48 hours after injection of 131I - HSA was reduced in animals treated with <span class="chemical">D - pen</span> for 42 days , indicating an impeded transmural transport of tracer which may be caused by a steric exclusion effect of abundant <span class="chemical">hyaluronate</span> . 