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: Another lesioning procedure , ventrolateral thalamotomy , has become a powerful alternative to stimulate the nucleus ventralis intermedius , producing high long - term success rates and low morbidity rates .
### Output Text:
Another lesioning procedure , ventrolateral thalamotomy , has become a powerful alternative to stimulate the nucleus ventralis intermedius , producing high long - term success rates and low morbidity rates . 