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: METHOD : The response of 44 patients meeting DSM - IV criteria for bipolar disorder to naturalistic treatment was assessed for at least 6 weeks using the Montgomery - Asberg Depression Rating Scale and the Bech - Rafaelson Mania Rating Scale .
### Output Text:
METHOD : The response of 44 patients meeting DSM - IV criteria for bipolar disorder to naturalistic treatment was assessed for at least 6 weeks using the Montgomery - Asberg Depression Rating Scale and the Bech - Rafaelson Mania Rating Scale . 