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: Twenty healthy male volunteers ( mean age 24 years ; range 18 - 38 years ) received intradermal injections of glutamate and capsaicin in the volar forearm .
### Output Text:
Twenty healthy male volunteers ( mean age 24 years ; range 18 - 38 years ) received intradermal injections of <span class="chemical">glutamate</span> and <span class="chemical">capsaicin</span> in the volar forearm . 