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 , the rat converts deoxycholic acid , a poor choleretic , to taurocholic acid , a good choleretic .
### Output Text:
Furthermore , the rat converts <span class="chemical">deoxycholic acid</span> , a poor choleretic , to <span class="chemical">taurocholic acid</span> , a good choleretic . 