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: Histopathological examination revealed many lipophages in the periorbital fat surrounding the optic nerve in 1 eye , indicative of phagocytosis of previously existing fat cells and suggesting prior fat necrosis .
### Output Text:
Histopathological examination revealed many lipophages in the periorbital fat surrounding the optic nerve in 1 eye , indicative of phagocytosis of previously existing fat cells and suggesting prior fat necrosis . 