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: On a low - salt ( LS ) diet , male DS had higher levels of intrarenal angiotensinogen mRNA than females .
### Output Text:
On a low - <span class="chemical">salt</span> ( LS ) diet , male DS had higher levels of intrarenal angiotensinogen mRNA than females . 