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: They were less likely to have a low body mass index , and more likely to have died in police custody , to have received medical treatment immediately before death , to have survived for a longer period , to have developed hyperthermia , and to have died in summer months .
### Output Text:
They were less likely to have a low body mass index , and more likely to have died in police custody , to have received medical treatment immediately before death , to have survived for a longer period , to have developed hyperthermia , and to have died in summer months . 