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: Furthermore , betaine ( 200 and 400 mg / kg ) treatment increased the ventricular expression of Bcl - 2 and reduced the level of Bax , therefore causing a significant increase in the ratio of Bcl - 2 / Bax .
### Output Text:
Furthermore , <span class="chemical">betaine</span> ( 200 and 400 mg / kg ) treatment increased the ventricular expression of Bcl - 2 and reduced the level of Bax , therefore causing a significant increase in the ratio of Bcl - 2 / Bax . 