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 previous experiments we found that decreases in food intake were induced by local administration of calcitonin into several hypothalamic sites and into the nucleus accumbens .
### Output Text:
In previous experiments we found that decreases in food intake were induced by local administration of <span class="chemical">calcitonin</span> into several hypothalamic sites and into the nucleus accumbens . 