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: Total cell yields from DES - treated pituitaries increased from 1 . 3 times control yields at 8 days of treatment to 58 . 9 times control values by day 150 .
### Output Text:
Total cell yields from <span class="chemical">DES</span> - treated pituitaries increased from 1 . 3 times control yields at 8 days of treatment to 58 . 9 times control values by day 150 . 