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: Over the long - term chronic phase ( 120 days after transplantation ) , only 25 % of BMC - treated epileptic animals had seizures , but with a lower frequency and duration compared to the epileptic control group .
### Output Text:
Over the long - term chronic phase ( 120 days after transplantation ) , only 25 % of BMC - treated epileptic animals had seizures , but with a lower frequency and duration compared to the epileptic control group . 