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: Germfree ( GF ) Lobund strain Wistar ( LW ) rats , fed vegetable diet L - 485 , have developed prostate adenocarcinomas spontaneously ( 10 % incidence ) at average age 34 months .
### Output Text:
Germfree ( GF ) Lobund strain Wistar ( LW ) rats , fed vegetable diet L - 485 , have developed prostate adenocarcinomas spontaneously ( 10 % incidence ) at average age 34 months . 