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: We measured the degree of morphologic damage by ultrastructural examination of endomyocardial biopsy and the degree of performance abnormally by right heart catheterization in patients receiving DXR .
### Output Text:
We measured the degree of morphologic damage by ultrastructural examination of endomyocardial biopsy and the degree of performance abnormally by right heart catheterization in patients receiving <span class="chemical">DXR</span> . 