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: Systemic application of KCN , to evaluate the effects of peripheral chemoreception activation on ventilation , led to a similar increase in VE for both groups .
### Output Text:
Systemic application of KCN , to evaluate the effects of peripheral chemoreception activation on ventilation , led to a similar increase in VE for both groups . 