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: These rats also showed gross enlargement of their livers and an increase in foci of cellular alteration , the latter also being observed in the low dosage male rats .
### Output Text:
These rats also showed gross enlargement of their livers and an increase in foci of cellular alteration , the latter also being observed in the low dosage male rats . 