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 enhancement of aminonucleoside nephrosis by the co - administration of protamine .
### Output Text:
The enhancement of <span class="chemical">aminonucleoside</span> nephrosis by the co - administration of protamine . 