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: A total of 60 male Wistar albino rats were randomly divided into four groups ( 15 / group ) : The control group injected with single doses of normal saline ( i . c . v ) followed 24 h later by BCNU solvent ( i . v ) .
### Output Text:
A total of 60 male Wistar albino rats were randomly divided into four groups ( 15 / group ) : The control group injected with single doses of normal saline ( i . c . v ) followed 24 h later by <span class="chemical">BCNU</span> solvent ( i . v ) . 