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: NS - 718 , a lipid nanosphere incorporating amphotericin B , is effective against pathogenic fungi and has low toxicity .
### Output Text:
NS - 718 , a lipid nanosphere incorporating <span class="chemical">amphotericin B</span> , is effective against pathogenic fungi and has low toxicity . 