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 hematologic effects of cefonicid and cefazedone in the dog : a potential model of cephalosporin hematotoxicity in man .
### Output Text:
The hematologic effects of <span class="chemical">cefonicid</span> and <span class="chemical">cefazedone</span> in the dog : a potential model of <span class="chemical">cephalosporin</span> hematotoxicity in man . 