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: Injections of ketamine in doses from 100 microgram to 3 mg into the artery produced a depression of the SA nodal activity by a direct action .
### Output Text:
Injections of <span class="chemical">ketamine</span> in doses from 100 microgram to 3 mg into the artery produced a depression of the SA nodal activity by a direct action . 