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 other animals locomotor activity was measured 15 or 60 min after caffeine administration .
### Output Text:
In other animals locomotor activity was measured 15 or 60 min after <span class="chemical">caffeine</span> administration . 