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 order to address long - term pain memory , nine healthy male volunteers received intradermal injections of three doses of capsaicin ( 0 . 05 , 1 and 20 microg , separated by 15 min breaks ) , each given three times in a balanced design across three sessions at one week intervals .
### Output Text:
In order to address long - term pain memory , nine healthy male volunteers received intradermal injections of three doses of <span class="chemical">capsaicin</span> ( 0 . 05 , 1 and 20 microg , separated by 15 min breaks ) , each given three times in a balanced design across three sessions at one week intervals . 