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: Myxedema coma is a life threatening condition that carries a mortality reaching as high as 20 % with treatment .
### Output Text:
Myxedema coma is a life threatening condition that carries a mortality reaching as high as 20 % with treatment . 