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: In the saline treated group , the first significant decline in passive avoidance response was observed at four weeks , and complete memory loss was found five weeks after the acquisition of the passive avoidance task .
### Output Text:
In the saline treated group , the first significant decline in passive avoidance response was observed at four weeks , and complete memory loss was found five weeks after the acquisition of the passive avoidance task . 