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: Doxorubicin treatment also caused a decrease in RCR for liver mitochondria ( 3 . 9 + / - 0 . 9 versus 5 . 6 + / - 0 . 7 for control rats ) and inhibition of hepatic cytochrome oxidase activity .
### Output Text:
<span class="chemical">Doxorubicin</span> treatment also caused a decrease in RCR for liver mitochondria ( 3 . 9 + / - 0 . 9 versus 5 . 6 + / - 0 . 7 for control rats ) and inhibition of hepatic cytochrome oxidase activity . 