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 data further suggest that the consolidation of this memory is an important interim stage , and may take up to one day .
### Output Text:
The data further suggest that the consolidation of this memory is an important interim stage , and may take up to one day . 