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: Mice ( n = 12 for each point ) received single IP injections of a fixed volume / g body weight of physiological saline carrier with or without caffeine in doses ranging from 125 - 500 mg / kg .
### Output Text:
Mice ( n = 12 for each point ) received single IP injections of a fixed volume / g body weight of physiological saline carrier with or without <span class="chemical">caffeine</span> in doses ranging from 125 - 500 mg / kg . 