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: METHODS : The son of an 84 - year - old male discovered a newspaper report stating clinical success with plant extracts in Alzheimer ' s disease .
### Output Text:
METHODS : The son of an 84 - year - old male discovered a newspaper report stating clinical success with plant extracts in Alzheimer ' s disease . 