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: Three series of experiments were performed on 30 WKY and 30 SHR , chronically instrumented with guide tubes in the lateral ventricle ( LV ) and arterial and venous catheters .
### Output Text:
Three series of experiments were performed on 30 WKY and 30 SHR , chronically instrumented with guide tubes in the lateral ventricle ( LV ) and arterial and venous catheters . 