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: Serum alpha - GST levels were significantly elevated by day 4 , which corresponded to hepatotoxicity as shown by the increasing incidence of inflammation of the liver capsule , necrosis , and steatosis throughout the study .
### Output Text:
Serum alpha - GST levels were significantly elevated by day 4 , which corresponded to hepatotoxicity as shown by the increasing incidence of inflammation of the liver capsule , necrosis , and steatosis throughout the study . 