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: Six - to 9 - month old rats receiving prenatal dexamethasone on days 17 and 18 of gestation had a 17 % reduction in glomeruli ( 23 380 + / - 587 ) compared with control rats ( P < 0 . 05 ) .
### Output Text:
Six - to 9 - month old rats receiving prenatal <span class="chemical">dexamethasone</span> on days 17 and 18 of gestation had a 17 % reduction in glomeruli ( 23 380 + / - 587 ) compared with control rats ( P < 0 . 05 ) . 