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: By using transthoracic echocardiography , anterior and posterior wall thickness , LV diameters and LV fractional shortening ( FS ) were measured in all rats before DOX or saline , and at weeks 6 and 9 after treatment in all surviving rats .
### Output Text:
By using transthoracic echocardiography , anterior and posterior wall thickness , LV diameters and LV fractional shortening ( FS ) were measured in all rats before <span class="chemical">DOX</span> or saline , and at weeks 6 and 9 after treatment in all surviving rats . 