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: Wistar rats ( n = 66 ) received DOX injections intraperitoneally and were randomly assigned to 2 experimental protocols : ( 1 ) rats were killed before ( - 24 h , n = 8 ) and 24 h after ( + 24 h , n = 8 ) a single dose of DOX ( 4 mg / kg body weight ) to determine the DOX acute effect and ( 2 ) rats ( n = 58 ) received 4 injections of DOX ( 4 mg / kg body weight / week ) and were killed before the first injection ( M0 ) and 1 week after each injection ( M1 , M2 , M3 , and M4 ) to determine the chronological effects .
### Output Text:
Wistar rats ( n = 66 ) received <span class="chemical">DOX</span> injections intraperitoneally and were randomly assigned to 2 experimental protocols : ( 1 ) rats were killed before ( - 24 h , n = 8 ) and 24 h after ( + 24 h , n = 8 ) a single dose of <span class="chemical">DOX</span> ( 4 mg / kg body weight ) to determine the <span class="chemical">DOX</span> acute effect and ( 2 ) rats ( n = 58 ) received 4 injections of <span class="chemical">DOX</span> ( 4 mg / kg body weight / week ) and were killed before the first injection ( M0 ) and 1 week after each injection ( M1 , M2 , M3 , and M4 ) to determine the chronological effects . 