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 lemon essential oils showed strong ability to improve memory impaired by scopolamine ; however , s - perillyl alcohol relieved the deficit of associative memory in PA only , and did not improve non - associative memory significantly in OFH .
### Output Text:
These lemon essential oils showed strong ability to improve memory impaired by <span class="chemical">scopolamine</span> ; however , <span class="chemical">s - perillyl alcohol</span> relieved the deficit of associative memory in PA only , and did not improve non - associative memory significantly in OFH . 