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: Without treatment , 73 of 92 animals ( 80 % ) died after injection of bovine serum albumin ( BSA ) on day + 7 of pertussis immunization .
### Output Text:
Without treatment , 73 of 92 animals ( 80 % ) died after injection of bovine serum albumin ( BSA ) on day + 7 of pertussis immunization . 