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: Preclinical toxicologic investigation suggested that a new calcium channel blocker , Ro 40 - 5967 , induced cardiovascular alterations in rat fetuses exposed to this agent during organogenesis .
### Output Text:
Preclinical toxicologic investigation suggested that a new <span class="chemical">calcium</span> channel blocker , <span class="chemical">Ro 40 - 5967</span> , induced cardiovascular alterations in rat fetuses exposed to this agent during organogenesis . 