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 addition , these data indicate a direct role of the pituitary in the augmentation of ketamine DOC induced by melatonin .
### Output Text:
In addition , these data indicate a direct role of the pituitary in the augmentation of <span class="chemical">ketamine</span> DOC induced by <span class="chemical">melatonin</span> . 