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: Bone marrow recovery and peripheral blood recovery were complete 1 month and 3 months , respectively , after treatment , and blood transfusion or other therapies were not necessary in a follow - up period of more than 2 years .
### Output Text:
Bone marrow recovery and peripheral blood recovery were complete 1 month and 3 months , respectively , after treatment , and blood transfusion or other therapies were not necessary in a follow - up period of more than 2 years . 