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: In normal rats , the media of small arteries ( 0 . 4 - - 0 . 2 mm in diameter ) previously was shown to contain intracellular vacuoles , identified ultrastructurally as herniations of one smooth muscle cell into another .
### Output Text:
In normal rats , the media of small arteries ( 0 . 4 - - 0 . 2 mm in diameter ) previously was shown to contain intracellular vacuoles , identified ultrastructurally as herniations of one smooth muscle cell into another . 