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: The new approach to ex vivo blood vessel experiments in which not only the end points of vessels response within the time interval is considered , but also dynamics of this response , was used in this paper .
### Output Text:
The new approach to ex vivo blood vessel experiments in which not only the end points of vessels response within the time interval is considered , but also dynamics of this response , was used in this paper . 