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: The lack of a significant increase in products of lipid peroxidation suggests that the oxidant stress is of insufficient magnitude to result in irreversible injury to hepatocyte cell membranes .
### Output Text:
The lack of a significant increase in products of lipid peroxidation suggests that the oxidant stress is of insufficient magnitude to result in irreversible injury to hepatocyte cell membranes . 