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: Male Sprague Dawley rats were treated with betaine ( 100 , 200 , and 400 mg / kg ) orally for 40 days .
### Output Text:
Male Sprague Dawley rats were treated with <span class="chemical">betaine</span> ( 100 , 200 , and 400 mg / kg ) orally for 40 days . 