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: This may indicate that an activation of the peripheral adrenergic mechanism plays an important role in the induction of the excitatory effect of ketamine injected in the SA node artery .
### Output Text:
This may indicate that an activation of the peripheral adrenergic mechanism plays an important role in the induction of the excitatory effect of <span class="chemical">ketamine</span> injected in the SA node artery . 