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 same DES treatment produced no significant growth ( 8 . 9 + / - 0 . 5 mg for treated females versus 8 . 7 + / - 1 . 1 for untreated females ) or morphological changes in Brown Norway ( BN ) rat pituitaries .
### Output Text:
The same <span class="chemical">DES</span> treatment produced no significant growth ( 8 . 9 + / - 0 . 5 mg for treated females versus 8 . 7 + / - 1 . 1 for untreated females ) or morphological changes in Brown Norway ( BN ) rat pituitaries . 