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: Second - and third - generation cephalosporins , especially cefotetan , are increasingly associated with severe , sometimes fatal immune hemolytic anemia .
### Output Text:
Second - and third - generation <span class="chemical">cephalosporins</span> , especially <span class="chemical">cefotetan</span> , are increasingly associated with severe , sometimes fatal immune hemolytic anemia . 