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 mean lowest BIS score corresponding to the ability of the patient to immediately repeat words read from the list was 77 . 1 ( 95 % CI = 74 . 3 to 80 . 0 ) .
### Output Text:
The mean lowest BIS score corresponding to the ability of the patient to immediately repeat words read from the list was 77 . 1 ( 95 % CI = 74 . 3 to 80 . 0 ) . 