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: CONCLUSIONS : There is a range of BIS scores during which sedated patients are able to repeat words read to them but are not able to subsequently recall these words .
### Output Text:
CONCLUSIONS : There is a range of BIS scores during which sedated patients are able to repeat words read to them but are not able to subsequently recall these words . 